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Cbautauqua IReaDing Circle Xiterature 



STUDY OF THE SKY 




HERBERT A. HOWE, A.M., Sc.D., 



Director of the Chamberlin Observatory, University of Denver ; author of 
"Elements of Descriptive Astronomy." 




MEADVILLE PENNA 

FLOOD AND VINCENT 

Cfoe (Cfmutauqua-Centurp pve$$ 

NEW YORK : CINCINNATI : CHICAGO : 

150 Fifth Avenue. 222 W. Fourth St. 57 Washington St 
1896 



V\«ll -^ 



•H-8S" 



Copyright, 1896 
By Flood & Vincent 



« 



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The Chautauqua- Century Press, Meadville, Pa., U. S. A. 
Electrotyped, Printed, and Bound by Flood & Vincent. 



TO HUNDREDS OF MY PUPILS, 

WHOSE STEADFAST DEVOTION 

TO THEIR DAILY TASKS 

IS A DELIGHTFUL MEMORY, 

THIS BOOK IS 

AFFECTIONATELY DEDICATED 



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The required books of the C. L. S. C. are recommended by a 
Council of six. It must, however, be understood that 
recommendation does not involve an approval by the Coun- 
cil, or by any member of it, of every principle or doctrine 
contained in the book recommended. 



PREFACE. 

Astronomy is at once the most ancient and the 
noblest of the physical sciences. For thousands of 
years successive generations of men have gazed with ad- 
miration and delight at the brilliant orbs which glitter in 
the diadem of night. The shining constellations, the 
roving planets, the ever-changing moon, the splendid 
Galaxy, a celestial river bedded by suns and banked by 
the ether, all these display their beauties before the 
ravished eye. 

"The sky 
Spreads like an ocean hung on high, 
Bespangled with those isles of light 
So wildly, spiritually bright. 
Who ever gazed upon them shining, 
And turned to earth without repining, 
Nor wished for wings to flee away, 
And mix with their eternal ray?" 

To the study of these inspiring objects our book is 
devoted. Their story is told with plainness and sim- 
plicity. The standpoint adopted is that of the astron- 
omer, who observes, records what he sees, studies his 
observations, digs out the truths which they contain, 
and weaves them into laws and theories which embrace 
the visible universe, reaching from unknown depths of 
past ages up to unmeasured heights of futurity. 

The historical development of the science is sketched. 
An explanation of the apparent daily motion of the 
heavens is given. The chief constellations are set forth 
in detail, that the learner may have ample guidance in 



vi Preface. 

his endeavors to become acquainted with them. The 
reader is introduced to the astronomer, inspects an ob- 
servatory, and becomes acquainted with the most im- 
portant instruments and their uses. Thus he is prepared 
to listen appreciatively to an unvarnished tale, in which 
are set forth the principal things which are known or 
reasonably surmised concerning the worlds around us. 

The effectiveness of the presentation of the subject is 
much enhanced by the illustrations, for many of the 
finest of which the thanks of both reader and author are 
due to the directors of the Lick and Harvard College 
Observatories, and to the editors of Popular Astronomy, 
Kiiowledge, and The Astrophysical Journal. 

Notice of any error will be gratefully received by the 
author, whose address is Chamberlin Observatory, Uni- 
versity Park, Colorado. 



CHAPTER 
I. 

II. 

III. 

IV. 

V. 

VI. 

VII. 

VIII. 

IX. 

X. 

XI. 

XII. 
XIII. 
XIV. 

XV. 

XVI. 

XVII. 

XVIII. 



CONTENTS. 

PAGE 

Introduction and Historical 

Sketch 15 

The Heavens and their Apparent 

Daily Revolution 36 

The Constellations in General . 48 
The Constellations for January 

and February 56 

The Constellations for March and 

April 79 

The Constellations for May and 

June 95 

The Astronomer 11 1 

A Great Telescope 128 

The Astronomer's Workshop, and 

Some of His Tools 143 

Time 167 

The Sun 179 

The Moon and Eclipses 205 

Mercury and Venus 231 

Mars and the Asteroids 236 

Jupiter, Saturn, Uranus, and Nep- 
tune 253 

Comets and Meteors 271 

The Fixed Stars 301 

The Nebulae 321 



DIAGRAMS AND ILLUSTRATIONS. 

The Moon Partially Eclipsed Frontispiece. 

FIGURE PAGE 

i. The Moon 19 

2. Cycle and Epicycle 25 

3. Tycho 28 

4. Kepler 30 

5. Galileo 31 

6. Sir Isaac Newton 33 

7. Laplace 34 

8. A Section of the Milky Way 37 

9. The Great Dipper 40 

10. Measurement of an Angle 41 

11. The Two Dippers 45 

12. Ursa Major . . . . 59 

13. Ursa Minor 61 

14. Cassiopeia 63 

15. Pegasus 65 

16. Aquarius 66 

17. Pisces 68 

18. Andromeda 70 

19. Aries 71 

20. Cetus 71 

21. Taurus 73 

22. Orion 75 

23. Auriga 77 

24. Gemini 80 

25. Perseus 82 

26. Cancer 83 

27. Canis Major 84 

28. Canis Minor 85 

29. Lepus 85 

30. Leo 86 

31. Bootes 88 

32. Virgo 90 



Diagrams and Illustrations. 



RE PAGE 

Corvus 91 

Corona Borealis 92 

Hydra 93 

Lyra 95 

Hercules 97 

Cygnus 98 

Draco 100 

Sagitta 101 

Scorpio 102 

Libra 103 

Delphinus 104 

Aquila 105 

Serpens and Ophiuchus 106 

Sagittarius . 108 

Cepheus 109 

Capricornus no 

Charles A. Young 112 

Edward S. Holden 114 

Simon Newcomb 115 

Benjamin A. Gould 116 

Edward C. Pickering 117 

William H. Pickering 119 

Edward E. Barnard 120 

James E. Keeler 121 

First Position of the Spider-webs 123 

Second Position of the Spider-webs 123 

A Micrometer 124 

Third Position of the Spider-webs 124 

Seth C. Chandler 125 

Sherburne W. Burnham 126 

The Yerkes Telescope at the Columbian Exposition . 129 

Alvan G. Clark 130 

Lump of Optical Glass 132 

The Lump Cut Down 133 

The Lump Molded 133 

The Lump after Further Cutting 134 

The Lump Cut Down Still More . . . 134 

Machine for Polishing Lenses 135 

Alvan Clark's Workshop 136 

John A. Brashear 137 



Diagrams and Illustrations. xi 

FIGURE PAGE 

73. The Two Lenses of an Object-Glass 138 

74. An Equatorial Telescope 139 

75. The Chamberlin Telescope of the University of Den- 

ver 141 

76. The Yerkes Observatory 144 

77. The Chamberlin Observatory 145 

78. Main Floor of the Chamberlin Observatory 147 

79. A Meridian Circle 150 

80. The Spider-webs 152 

81. The Spire on the Cross Wires 153 

82. The Lick Observatory 155 

83. A Chronograph 157 

84. A Portion of a Chronograph Sheet 158 

85. The Lick Micrometer 159 

86. Measurement of a Planet's Diameter 160 

87. Bisection by Spider-webs 161 

88. Essentials of a Spectroscope 162 

89. A Spectroscope 165 

90. A Watch Balance 177 

91. Sun-spots 183 

92. Changes in a Solar Spot 184 

93. A Portion of the Photosphere 187 

94. Faculcs 190 

95. Prominences 191 

96. A Quiescent Prominence 192 

97. The Corona of July, 1878 194 

98. The Corona of January, 1889 195 

99. The Corona of April, 1893 196 

100. Lunar Formations 207 

101. Lunar Plains, called Seas 210 

102. Copernicus 213 

103. The Apennines 216 

104. The Mare Crisium 219 

105. A Rugged Region near Tycho , 223 

106. Moon's Shadow on the Earth, as seen from the Moon, 227 

107. Conjunction and Elongation 232 

108. Markings on Venus 235 

109. Mars 236 

no. Projections on the Polar Cap 238 

in. The Lake of the Sun 239 



xii Diagrams and Illustrations. 

FIGURE . PAGE 

112. Canals 241 

113. Projections on the Edge of the Disc 242 

114. Canals connected with Lacus Solis 243 

115. The Polar Cap in July and August, 1892 244 

116. Canals in August, 1892 245 

117. The Cap Diminishing, August 24-9, 1892 246 

118. Asteroid Trail on a Photograph of the Pleiades . . . 249 

119. Jupiter 254 

120. The Great Red Spot 256 

121. Saturn 261 

122. Sir William Herschel 266 

123. Discover}' of a Comet by Photography 272 

124. Paths of Comets 273 

125. Jets and Envelopes 276 

126. Photographs of Swift's Bright Comet of 1892 .... 279 

127. Holmes's Comet 282 

128. Photograph of Rordame's Comet, showing Masses 

of Matter driven off into the Tail 285 

129. Comet c, 1893 (Brooks) 287 

130. A Besprinkling , 290 

131. Photograph showing a Meteor's Path among the 

Stars 293 

132. A Meteorite seen July 27, 1894 298 

133. Outlines of Dark Structures in the Galaxy 302 

134. A Part of the Milky Way in Cygnus 304 

135. Motion of the Components of a Double Star .... 308 

136. A Rich Portion of the Milky Way 312 

137. The Great Globular Cluster in Hercules 315 

138. Cloudy Region in the Milky Way 318 

139. A Spiral Nebula 322 

140. The Nebula of Orion Photographed. Exposure, 

fifteen minutes 324 

141. The Nebula of Orion Photographed. Exposure, two 

hours 324 

142. The Nebula of Orion Photographed. Exposure, nine 

hours 3 2 5 

143. A Drawing of the Central Part of the Great Nebula 

in Orion 329 

144. The Ring Nebula in Lyra 334 



A STUDY OF THE SKY. 
CHAPTER I. 

INTRODUCTION AND HISTORICAL SKETCH. 

" The heavens declare the glory of God : 
And the firmament sheweth his handy work." 

The starry spheres which roll and shine, uncounted 
millions, in the infinite depths of space call us away Thestarr 
from the common things of earth, and bid us plume our s P heres - 
spirits for the loftiest flights. Not in the garish glory of 
the day, when men's eyes are well-nigh blinded by the 
affluence of light which the sun pours forth, and their 
minds are caged in the narrow round of daily toil, are 
the wonders of the sky revealed. But when the clangor 
and roar of the world's traffic have died away, and the 
last glint of the retiring sun has vanished from the 
mountain top ; when the soft shades of the evening twi- 
light gradually melt into the darkness of the night, and 
the blessed shadow of the earth steals over the abodes of The blessed 
men, bringing rest and refreshment of mind, then come 
forth the troops of radiant orbs, filling the sky with their 
splendid array, and giving to the mind of the beholder 
a portion of their own eternal calm. 

" The starry skies, they rest my soul, 
Its chains of care unbind, 
And with the dew of cooling thoughts 
Refresh my sultry mind. 

" And like a bird amidst the boughs 
I rest, and sing and rest, 
Among those bright dissevered worlds, 
As safe as in a nest." 



i6 



A Study of the Sky. 



Mysteries are 
unraveled. 



Powerful 
instruments. 



With this calmness of mind comes reflection, followed 
by a keen thirst for knowledge. The enigma of the 
universe is thrust upon the beholder, and he accepts the 
challenge to solve it. Year after year, century after 
century, has the dauntless mind of man climbed the 
arduous steep which leads to a knowledge of the stars. 
Each defeat has stimulated it to greater exertions and 
more glorious victories. Barrier after barrier has been 
surmounted or broken down. Difficulty after difficulty 
has vanished before persistent effort. 

Ingenious and powerful instruments have been de- 
vised, which reveal wonders otherwise unimagined, and 
the end is not yet. Each new telescopic giant is ex- 
pected to win fresh laurels in old fields of endeavor, or 
to make discoveries which shall link its name forever 
with the stars. When the great thirty-six-inch glass, 
the fame of which has spread throughout the world, was 
set up on Mt. Hamilton, a poet's fancy was stirred, and 
he addressed the ensuing lines to the lens.* 

' ' Perchance that thou 
With cloudless vision slowly sweeping up 
The mighty Nave that cleaves the Galaxy — 
God's visible Tabernacle in the skies, 
Star-built from shining undercroft to dome, 
Past pillared pomp of worlds, and columns wrought 
With fair entangle of amethyst and pearl, 
Thro' jacinth portals hung with mist of stars, 
And fiery fringe of suns — mayst come at last 
Even to the chancel of the Universe ; 
And so thro' glories veiled and far, behold 
The Choral Stars that sang so loud and sweet 
On the first morning when creation sprang 
In dewy beauty from Jehovah's hand. 
Mayhap that thou, with swiftness unconceived, 
Wilt overtake the light and see the things 



* " Handbook of the Lick Observatory," page 76. 



Introduction and Historical Sketch. 17 

That have been, and that shall be nevermore ; 
Follow the dying star in her swift flight 
Athwart Eternity ; track the lost world, 
That drifting past our ken, still gleameth fair 
Upon the confines of some far-off realm ; 
Perchance the Star which first spake peace to men 
Will dawn through thee upon the waiting earth ; 
And O far-seeing Eye, perchance mayst thou 
Reveal the City Beautiful which lies 
Four-square in midst of heaven, whose shining walls 
Are of fair jasper builded and pure gold ; 
Whose battlements are crystal and whose ways 
Are sapphire paven, and whose gates are pearl." 

No astronomer has any expectation of such good for- 
tune as the poet has outlined. But the spacious firma- God is aJeSty ° 
ment, to the study of which he gives his nightly vigils revea e 
and his daily toils, is the handiwork of the Most High, 
and continually reveals to the earnest student the 
majesty and glory of the omnipotent, the ever-living 
God. 

Many and toilsome have been the steps by which the The ladder of 
astronomers of centuries past and present have mounted P r °s ress - 
the long ladder whose base rests on the earth, and whose 
summit is now to be found among the star-clouds of the 
Milky Way. 

The first astronomer was Adam : his observatory was 
one of the flower-decked mounds of the Garden of Eden, astronomer. 
His two telescopes were fresh from a celestial workshop. 
What must have been his feelings as the glowing orb of 
day, which had warmed his body and cheered his spirit, 
sank in the west and the evening twilight deepened ! 
Was he to be imprisoned in a dungeon of darkness, and 
the beautiful creation about him to fade into nothingness ? 

Behold ! a new light appears in the sky ; the silvery 
moon, which has been appointed to rule the night, 
stands out in all her beauty, and casts dim shadows of 



i8 



A Study of the Sky 



The moon and 
stars appear. 



The Milkv 
Wav. 



Adam sleeps 
and wakens. 



the foliage on the darkening turf. But hers is not the 
only light. Here and there, scattered over the broad 
expanse of the sky, appear the brighter stars, set like 
jewels as a crown upon earth's brow. They have 
various colors and degrees of brightness : a multitude of 
lesser lights gradually come forth, forming strange con- 
figurations. Now, for the first time, the solitary observer 
notices that the moon is following the sun to a grave 
in the west, and that the stars too are joining in the gen- 
eral movement. Will all at last be lost to his vision, 
and darkness rule supreme ? He faces eastward and 
sees new groups of stars rising to take the places of 
those which are passing away. The moon sinks in the 
west ; earnestly he watches the glow on the horizon at 
the point where she disappeared, until it fades away. 

Upward again he throws his inquiring glance, and be- 
holds the most wonderful sight of all. Athwart the star- 
sphere a broad river of light pursues its tortuous way. 
In places it glows as if pent-up fires were about to burst 
forth ; in other places are black rifts, which seem to in- 
tensify the darkness of the night. Upon all nature has 
fallen a solemn hush, broken only by the faint notes of a 
far-away nightingale. A strange drowsiness creeps over 
our great ancestor and fills him with dread : in vain he 
fights against it : overcome he sinks down and is lost in 
slumber. What visions may have come to him we know 
not. The hours roll on, and the stars keep silent vigil 
over the slumberer : at last the aurora of approaching 
day glows along the eastern horizon. He awakens and 
feels the pleasurable glow of fresh life and vigor. The 
stars fade from view, and the first glint of the glad sun- 
shine greets his vision. The sun arises in its full glory, 
and animate nature is awakened. The man wonders 
and adores. Surelv he will be a lover of nature for life. 



Introduction and Historical Sketch. 19 

The majestic revolution of the heavens, the waxing and 
waning of the moon, the movements of the brilliant 
planets, an occasional outburst of a comet, all these will 




Fig. i.— The Moon. 

continually delight him, and will ever lead to fresh 
adoration of his Creator. 

How rudely are our bright expectations of Adam's The first appu 
astronomical joys shattered ! For a rationalistic instruc- scientific 
tor in the domain of theology, the wily serpent, took 



A step forward. 



20 A Study of the Sky. 

Adam and his companion in hand. Under his tuition 
they introduced the genuine scientific method of investi- 
gation, the method of experiment and observation, into 
fields theological. Inestimable as may be the value of 
this method, it brought ruin and desolation to the first 
experimenters. 

Brought sharply to his senses by being driven from 
his beautiful dwelling place, forced to earn his subsist- 
ence by the sweat of his brow, burdened with increasing 
cares and sorrows, Adam's spirit was much broken, and, 
like Bunyan's man with a muck-rake, he acquired the 
habit of looking downward instead of upward. 

We must take a long step forward to find the first 
glimmerings, more or less historic, of the lamp of 
astronomical knowledge. We thus emerge from the 
realm of fancy in which we have disported ourselves for 
a time into the dim borderland, in which history and 
myth are interwoven, and we shall press on speedily 
into the full light of historic fact. 

Among the first of astronomical allusions are those con- 
tained in the writings of the early Aryans, by whom the 

"Rigveda." hymns of the " Rigveda " were written. These writings, 
however, serve only to reveal to us primitive notions 
about the earth and the firmament, and do not contain 
astronomical observations. The earth is represented as 
a flat surface, on whose broad expanse rests the blue 
and ever-changing vault of heaven. Below this star- 
spangled vault is the home of the life-giving light. 

Josephus states that one reason why the lives of the 

josephus. antediluvian patriarchs were prolonged was that they 

might perfect the sciences of geometry and astronomy, 
which they had discovered. He also informs us that 
these primitive scientists had learned from Adam that 
the world was to perish by water and by fixe ; fearing 



The 



Herodotus. 



Introduction and Historical Sketch. 21 

therefore that the results of their centuries of labor 
would be lost, they built two columns, one of brick and 
the other of stone, which bore inscriptions intended to 
preserve the knowledge which their toil had wrested 
from the sky. In case the deluge destroyed the brick 
column, the stone one at least would come through un- 
harmed. Josephus would have us believe that the stone 
monument was still to be seen in his day. 

Herodotus, the father of history, makes the astonish- 
ing statement that the Egyptians had made astronomical 
observations for 11,340 years, and had seen the earth's 
equator perpendicular to the plane of its orbit. But the 
present refinement of astronomical theory forbids a belief 
that the equator and ecliptic have been perpendicular 
within the memory of man, and lends no countenance to 
the theory that they ever were. 

A high antiquity is claimed for the beginning of 
astronomy among: the Chinese. Forty-five centuries Early Chinese 

J ° m J . astronomy. 

ago the emperor Hoang-Ti is reputed to have built an 
observatory, and to have appointed an astronomical 
board, upon the members of which devolved the duties 
of regulating the times of the religious festivals. The 
ancient chronicles also relate that once upon a time the 
astronomical board, which consisted of two learned 
gentlemen bearing the rather hilarious names of Hi and 
Ho, forgot the dignity of its high position, and indulged 
in riotous living. Meanwhile the moon stole a march 
on the board, and eclipsed the sun. China was thus 
exposed to the wrath of the gods, because the eclipse 
had not been foreseen and the proper religious rites 
observed. The emperor at once accepted the resigna- 
tion of the board, by the sword of the executioner. 
The Chinese astronomical records of the past twenty-six 
centuries are thought to be fairly reliable ; they contain 



22 



A Study of the Sky. 



Babylonian 
astronomy. 



Grecian 
philosophers. 



Pythagoras. 



accounts of the appearances of remarkable comets, as 
well as data concerning eclipses. 

We must look to the plains of Babylonia for the most 
valuable early observations. The mild climate and open 
sky of Central Asia favored the development of the 
science of the stars. We are not surprised, then, to 
find that the Chaldeans were acute and patient observers 
through many generations, and accumulated a very 
respectable store of observational knowledge. Their 
greatest achievement lay in the line of observations of 
eclipses of the sun and moon. By careful study of the 
times at which eclipses had happened, they discovered 
that those phenomena repeated themselves in cycles of 
about eighteen years. Thus they were enabled to fore- 
tell eclipses with considerable accuracy. But of the 
real causes of those interesting phenomena they were 
ignorant. 

To the ancient Greeks modern astronomy owes a 
great debt. So sublime and mysterious are the 
heavenly bodies, and so intricate their motions, that 
the speculative minds of the early Grecian philosophers 
were irresistibly attracted to a study of them. Though 
many of their theories were groundless, and many of 
their statements obscure and mingled with metaphysics 
in a most curious fashion, yet gems of truth are to be 
found here and there, which well repay the labor spent 
in searching them out. 

Though Plato suggested that the world was a cube, 
which seemed to him the most perfect of solids, 
Eudoxus, Archimedes, and Aristotle made it a sphere. 
Nicetas is said to have ascribed the apparent daily 
revolution of the celestial sphere to the revolution of the 
earth upon its axis. 

To Pythagoras is attributed the beautiful but utterly 



Introduction and Historical Sketch. 23 

erroneous doctrine of the crystalline spheres. In the 
outermost of these were set the fixed stars, which had, 
long before his time, been grouped in constellations, and 
associated with mythological characters. Each planet 
too had its sphere. To him also is ascribed the theory 
that the sun is the center about which the earth and the 
other planets move ; this would nowadays be called 
a " class-room theory," because it was not promulgated 
except in a private way among his students. Philolaus, 
a follower of Pythagoras and a contemporary of Socrates, 
taught the doctrine openly. 

But the overwhelming influence of Aristotle soon Aristotle 
erased it from the Greek mind. He placed the earth 
immovable in the center of the universe, and did not 
allow it to rotate upon its axis. The celestial bodies 
were permitted to revolve around the earth in decorous 
fashion. So powerful was the influence of this intellec- 
tual giant upon the minds of thinking men for centuries 
afterward, that the earth was not finally and forever dis- 
placed from the erroneous position which he assigned to 
it till the days of Copernicus. 

To the second century before Christ belongs Hippar- Hipparchus 
chus, justly called the father of astronomy, who rescued 
Greek astronomy in large measure from the bog of spec- 
ulation into which earlier philosophers had plunged it, 
and made it a science of observation as well as of theory. 
He was a genius of the highest order, being at once an 
accurate observer of the celestial bodies, a profound 
mathematician, and a brilliant theorist. He devised the 
system of locating places on the earth by means of their 
latitude and longitude. In order to facilitate his compu- 
tations he invented that branch of mathematics now 
called trigonometry. The first catalogue of the fixed 
stars is due to his labors. The apparent motions of the 



24 



A Study of the Sky. 



Ptolemy. 



The shape of 
the earth. 



The earth's 
place. 



sun and moon he explained by an ingenious theory, 
which he tested by observation and computation. In 
determining the length of the year he made an error of 
only four minutes. 

After Hipparchus the most distinguished astronomer 
of antiquity was Ptolemy, who lived at Alexandria in the 
second century of our era, and wrote the "Almagest," 
which has come down to us entire, and in which is pre- 
served nearly all our knowledge of Greek astronomy. 
As the Ptolemaic system was the orthodox astronomy of 
the next fourteen centuries, we notice a few of its chief 
principles. 

The earth, said Ptolemy, must be round. For if one 
go southward new stars appear above the southern hori- 
zon, and stars in the north seem nearer the horizon than 
before. Besides this, the heavenly bodies do not rise at 
the same moment for two observers, one of whom is east 
of the other. Furthermore, when a sailor approaches 
the coast, the bases of the headlands are at first hidden 
from view by reason of the curvature of the sea. 

The earth must also be in the center of the celestial 
sphere, for if it were nearer to the eastern portion of the 
heavens than to the western the stars in the east would 
seem to move with greater rapidity than those in the 
west. Since the stars sweep across the sky each day at 
a perfectly regular rate, the earth must be equally dis- 
tant from all of them, and thus in the center of the uni- 
verse. 

What is the shape of the curve in which every 
heavenly body moves? Ptolemy replies that it is a 
circle, the most perfect of all curves. Now an objector 
might say that this would do for the fixed stars, the sun, 
and the moon, which move with exceeding regularity, 
but how could it explain the apparent motion of Saturn, 



Introduction and Historical Sketch. 



25 




or of Jupiter, both of which move irregularly ? Here 
Ptolemy had recourse to the device of the epicycle, in- 
troduced by Hipparchus. The word epicycle is derived 
from two Greek 
words, meaning 
' ' up on" and ' ' a 
circle." The epicycle 
was a circle the center 
of which moved along 
the circumference of 
another circle. The 
idea is easily grasped 
by reference to Fig. 2. 
E represents the earth; 
Jupiter, located at J, 
moves uniformly 

around the circumfer- FlG - 2 --Cvcle and Epicycle. 

ence of the small circle, while P, the center of that cir- 
cle, moves along the circumference of the large circle. 

Ptolemy found, by comparing his observations with 
those of Hipparchus, that he could not explain the 
motions of the sun, moon, and planets with sufficient 
accuracy by so simple a device. But by adding ad- 
ditional epicycles, and by placing the earth at a short 
distance from the center of the large circle in the dia- 
gram, he could explain the irregularities which per- 
plexed him. 

After Ptolemy's death the study of astronomy grad- 
ually declined, and suffered a decided set-back in the 
burning of the great library at Alexandria, in the middle 
of the seventh century. To the Arabians, who now 
made Bagdad the literary center of the civilized world, 
we must look for the next advances. They were assid- 
uous observers, and thus furnished a groundwork of fact 



Cycles and 
epicycles. 



Arabian 
astronomy. 



26 



A Study of the Sky. 



upon which later generations might build theories, and 
by which those theories might be tested. 

At last the intellectual aspirations of the peoples of 
The awakening Western Europe were awakened, after a slumber of cen- 

of Western _ l 

Europe. turies. The lamp of learning, which was burning in the 

Moorish universities of Spain, shed its beneficent rays 
among more northern nations. The Arabic version of 
Ptolemy' s ' ' Almagest ' ' was translated into the Latin 
language in the thirteenth century, under the patronage 
of Frederick II., emperor of the Holy Roman Empire. 
In the same century Alphonso X., king of Leon and 
Castile, who was surnamed "The Wise" and also 
" The Astronomer," published the celebrated Alphon- 
sine tables, which were prepared with immense labor 
by the best mathematicians of the Moorish universities. 
Observations were at this time so much more accurate 
and numerous than in the days of Ptolemy that many 
epicycles had to be added to the original system, in 
order to make theory correspond with observation. The 
entire heavens were said to be 



Alphonso's 
remark. 



Copernicus. 



" Scribbled o'er 
With cycle upon epicycle, orb on orb." 

So complicated had the celestial machinery become 
that Alphonso is said to have told a notable gathering 
of bishops that if the Almighty had done him the honor 
to consult him concerning the mechanism of the uni- 
verse, he could have offered some good advice. This 
irreverent remark may have been inspired by the de- 
pleted condition of the royal purse after the publication 
of the tables. 

Three centuries had yet to roll away before deliver- 
ance from the thraldom of Ptolemy came. On February 
12, 1473, Nicholas Copernicus was born at Thorn in 



Introduction and Historical Sketch. 27 

Prussia. During thirty-six of the seventy years that 
were allotted to him he studied the motions of the 
planets. Throughout a large part of his life he held 
high ecclesiastical rank as canon of Warmia, and had 
leisure for his favorite investigations. The variations in 
the brightness of Mars in different parts of its orbit were 
so great as to lead him to think that the earth could not 
be the center about which Mars revolved. The results 
of his meditations are set forth in the following transla- 
tion of his own words : 

And I too, on account of these testimonies, began to meditate 
upon the movement of the earth, and though that theory seemed Jheo" ew 
absurd, I thought that as others before my day had devised 
a system of circles to account for the motion of the stars, I also 
might endeavor, by supposing that the earth moved, to find a 
more satisfactory scheme of the movements of the heavenly 
bodies than that which now contents us. After long research I 
have become convinced that if we assume the revolution of the 
earth to be the cause of the wanderings of the other planets, 
observation and calculation will be in better agreement. And 
I doubt not that mathematicians will be of my opinion, if they 
will take pains to examine carefully and thoroughly the demon- 
strations to be given in this book. 

Copernicus broke with the Ptolemaic theory at two 

T T . , . , r 1 1 The new vs. the 

points. He placed the sun in the center 01 the planetary old. 
system, and explained the diurnal rotation of the 
heavens by the revolution of the earth on its axis. For 
a long time he hesitated about publishing the new doc- 
trines, knowing that they would at once make him 
a target for the ridicule and abuse of the unthinking and 
of the narrow-minded. 

The insistence of his warmest friends, particularly of 

1 . , J His work is 

the bishop of Culm, finally led to the publication of his published, 
great work, which was entitled " De Revolutionibus 
Orbium Ccelestium." It may well be called the Magna 



28 



A Study of the Sky. 



its importance. Charta of astronomical science. Copernicus did not live 
to see the reception which was accorded it ; the first 
copy, fresh from the press, was placed in his hand only 
a few hours before his death. In one important particu- 
lar Copernicus failed to break with Ptolemy ; he still re- 
tained the system of epicycles, but the innovations 

which he introduced 
simplified it greatly. 
The new system 
was soon to be put 
to a much more 
searching test than 
Ptolemy's had been 
subjected to. In 
1546, three years 
after the death of 
Copernicus, there 
came into the family 
of a Danish noble- 
man a son, who 
afterward became 
the famous Tycho 
Brahe. In those 
days it was little 
short of a misdemeanor for a member of an aristocratic 
family to engage in scientific researches ; to hunt ani- 
mals and to kill men according to the canons of war 
were the proper pursuits. The young noble was there- 
fore destined for the army. 

When but fourteen years of age Tycho' s curiosity was 

An eclipse. aroused by the occurrence of an eclipse. From that 

time forth his mind was with the stars. Sent to Leipzig 

to study law, he could not be induced to devote himself 

to it ; his money was spent for astronomical books and 



Tvcho Brahe. 




Fig. 3.— Tycho. 



Introduction and Historical Sketch. 29 

instruments, and his time was largely engrossed with 
observations of the stars. In 1563 he observed a con- 
junction of Jupiter and Saturn, which he thought to be 
the cause of the Great Plague. As the Copernican 
tables did not give the time of the conjunction accurately 
he resolved to make new ones. He constructed instru- 
ments of large size, and began to observe with fresh 
vigor. The king heard of his doings, and offered him a 
site for an observatory, ^20,000 for the building, and 
a life pension of ^400. The observatory, which was 
called Uranienburg (the Castle of the Heavens), was uranienburg. 
erected on the island of Huen, near Copenhagen. It 
was stocked with the largest and finest instruments 
which the mechanics of that day could build. For 
twenty years he worked with the utmost ardor, accumu- 
lating a vast store of observations of far greater accuracy 
than any which had been made previously. Of the 
subsequent death of his patron, his own impoverishment 
and virtual banishment, we may not give the details. 
On October 24, 1601, he died, after a painful illness, 
during which he frequently called out, ' ' Ne frustra 
vixisse videar " (May I not seem to have lived in vain!). 

Two years before Tycho's death, Johann Kepler Kepler, 
became his pupil. Tycho was one of the greatest of 
observers, but his pupil was preeminent as a theorist. 
Taking up Tycho's observations of Mars he endeavored 
to discover the laws of the planet's movement. Hy- 
pothesis after hypothesis was tried and rejected ; at one 
moment he was at the summit of hope ; at another he 
was in the depths of disheartenment. Struggling with 
indomitable perseverance against sickness, poverty, and 
misfortune, harassed by domestic troubles, and hampered 
at every turn, he pressed on through weary years to 
final victory. 



3o 



A Study of the Sky 



Kepler's laws. 



His exultation. 



Galileo. 



Three laws came to light through his labors : 

Law I. Each planet moves in an ellipse, at one focus 

/"": ■"- ' " " — — ~^™\ of which is the 



/ \ sun. 

\ Law II. The 

j 1 i n e j o i n i n g a 
% j planet to the sun 

! sweeps over equal 
1 areas in equal 
J times. 

j Law III. The 
| squares of the 
times of revolu- 
[ .. tion of any two 

■vHflfcrifc \ikM iJMMMillMWlfeir " * P^ anets are t0 

each other as the 

Wm cubes of their 

^| * mean distances 

from the sun. 

^ ^KKkKKIHHKKKKSKf Upon the dis- 

Fig. 4.— Kepler. CO very of the 

third law his exultation knew no bounds, as the follow- 
ing exclamation shows : 

Nothing holds me : I will indulge in my sacred fury : I will 
triumph over mankind by the honest confession that I have 
stolen the golden vases of the Egyptians to build up a taber- 
nacle for my God far away from the confines of Egypt. If you 
forgive me, I rejoice : if you are angry, I can bear it : the die 
is cast, the book is written, to be read either now or by poster- 
ity, I care not which : it may well wait a century for a reader, 
as God has waited six thousand years for an observer. 

While Kepler was making his immortal studies in 
theoretical astronomy, the science of observation took a 
tremendous stride. Galileo, then a professor in the 
University of Padua, heard that a Dutch spectacle-maker 



Introduction and Historical Sketch. 31 

had found a combination of glasses through which the 
weathercock on the church spire looked larger. Being 
familiar with the laws of optics he began to ponder over 
the matter. All night long he sat in a brown study ; by 
morning the solution came, and he soon had an old 
organ pipe with a glass at each end, which was the fore- 
runner of the great telescopes of our day. The Senate 
doubled his salary, and he went at telescope-making in 
earnest ; having completed one which magnified thirty 
times he began to explore the heavens. 

The moon displayed to him the rocky ramparts and Discoveries, 
battlemented crags of her mountains. The Milky Way 
was resolved into countless stars ; 

"Infinity's illimitable fields, 
Where bloom the worlds like flowers about God's feet." 

Jupiter was found to be attended by four moons, the en- 
tire system being a miniature of the solar system. The 
motions of these 

bodies powerfully ^^ 

confirmed the the- •§ 

ories of Coperni- 
cus. The surface >•;* 
of the sun was seen 
to be marred by \ 
spots. Venus be- 
came a waxing and 




The Aristoteli- 
ans were con- 
founded again and 

„■ t) j. J.T. Fig. s. — Galileo. 

again. But they ° 

had their revenge upon this pestilent fellow, who was 

turning the world of natural philosophy upside down. 

The hand of the Inquisition was laid upon him. But inquisition. 



32 A Study of the Sky. 

why relate the painful tale of the rigorous examinations, 
and the recantation finally forced upon the feeble old 
man? In the year 1642 the shattered body of the 
philosopher was laid to rest, but in unconsecrated 
ground, for the iron heel of the Inquisition must even 
grind his bones ! Many of his manuscripts were de- 
stroyed, and his friends were not permitted to raise a 
monument in his honor. 

But the truth, which had thus been ruthlessly trampled 
triumphant. under foot, beneath the blue skies of fair Italy, rose in 
adamantine strength amid the sturdy oaks of old Eng- 
land. On Christmas Day of the year in which Galileo 
died there was born a boy who was to supplement the 
work not only of Galileo, but also of Copernicus, Tycho, 
and Kepler, and to be recognized as the master mind 
among the world's philosophers. 

Isaac Newton was not a very promising lad, until the 
day when a bigger boy conferred a signal blessing on 
Isaac Newton. foe WO rld by kicking him. Young Isaac retorted by 
thrashing his assailant, and then proceeded to show the 
rest of the boys at school that he could beat them in 
their studies. So keen became his interest in books 
that he was sent to Trinity College, Cambridge, where 
his remarkable aptitude for mathematics displayed itself. 
We cannot recount all the marvelous researches to 
which Newton's genius lent itself. The discovery which 
concerns us at present is that of the law of gravitation. 

Copernicus had proved that the planets revolved 
about the sun as a center. Tycho had observed with 
all assiduity, and Kepler, by discussing these observa- 
tions, had discovered the three laws which bear his 
name. Galileo had not only enlarged astronomical 
knowledge by the use of the telescope, but had pro- 
mulgated the laws of motion of bodies on the surface of 



Introduction and Historical Sketch. 33 

the earth. These laws were admirably restated by 
Newton, and are now called Newton's laws. But the Newton's 
crowning glory of his achievements is the proof that the 




Fig. 6.— Sir Isaac Newton. 

same force which pulls the apple to the earth controls 

the motion of the moon, and binds the planets to the gravitation. 

sun. This force is not constant in intensity, but varies 

inversely as the square of the distance. Kepler's laws 

have been proven to be necessary consequences of the 



34 



A Study of the Sky. 



Its wide 
application. 



law of gravitation. The entire mechanism of the plane- 
tary movements, not their elliptical paths alone, but also 
their small departures from true ellipses, caused by their 




Fig. 7.— Laplace. 

attractions for one another, are all explained by this 
simple law. 

If Newton's law be correct, will not the mutual attrac- 
tions of the planets so derange their orbits that at last 



Introduction and Historical Sketch. 35 

there will be wreck and ruin, where now are order and 
beauty? During the last century Lagrange and La- Lagrange and 
place, the most illustrious of French mathematicians, 
proved that though the orbit of each planet alters some- 
what, changing in both shape and position, the disturb- 
ances are confined within narrow limits, and the system 
of planetary worlds is therefore stable. 

We now bring our rough historical outline to an end, 
having come up to the close of the eighteenth century, 
when the construction of large telescopes by Sir William 
Herschel and others gave a special impetus to observa- 
tional astronomy, and led to the unfolding of the science 
along new lines. 



William 
Herschel. 



The arm-chair. 



Bright stars. 



CHAPTER II. 

THE HEAVENS AND THEIR APPARENT DAILY REVO- 
LUTION. 

" The sad and solemn night 
Has yet her multitude of cheerful fires ; 
The glorious host of light 
Walk the dark hemisphere till she retires : 
All through her silent watches, gliding slow, 
Her constellations come, and climb the heavens, and go." 

Permit the author to talk to you, the reader, for a 
moment. Perchance you are seated in an arm-chair, 
with your feet on the fender, and this book in your 
hands. You have vanquished Chapter I. and are ready 
for fresh victories. The next foe to be overcome is the 
arm-chair. For you will never take a deep interest in 
astronomy if you confine yourself to an arm-chair and a 
book. A young man rarely becomes enamored of a 
young lady into whose face he has never gazed. You 
must look into the eyes of the goddess Urania ; they 
spangle the heavens, and will well repay your most 
ardent gazing. Surely you know the Great Dipper, 
which performs the endless round of motion about the 
north pole of the sky. But are you acquainted with 
Vega the beautiful, Arcturus the magnificent, Capella 
the icy, and Sirius the glowing ? Why do we call Vega 
beautiful? When you have observed its hue, you will 
know. Why is Arcturus magnificent ? If you shall be 
led to think that it is thousands of times as large as our 
sun, you will not begrudge it the adjective. In the dead 

36 



The Heavens and their Apparent Revolution. 37 

of winter look up through the frosty air at Capella, as it 
stands at the apex of the starry vault, shining with a 
clear white light. You will be ready to admit that it is 
a fit jewel for the crown of the ice-king. As soon as 
your. own eyes have marked the fact that Sirius is, in 
point of brightness, a seven-fold Vega, its splendid scin- 
tillations will 
glow in your 
memory. 

Have you seen 
that storehouse 

of Uncreated I I Nebulseand 

i 1 HhbI SSsBb*^ ms8§flt£&BB 5 clusters. 

worlds, the 
great nebula in 
Andromeda ? 
Have you at 
anytime turned 
your opera- 
glass upon the 
famous double 
cluster in Per- 
seus, or upon 
the Pleiades? 
How many stars 
can you see 
within the bowl 
of the Great 

_ . Fig. 8.— A Section of the Milky Way. 

Dipper ? Is 

your eye sufficiently keen to split the double-star Ep- 
silon Lyrae, which lies but three moon-breadths from 
Vega ? Has a telescope ever split again each of these 
stars for you, so that you realized that they formed a 
system of four revolving suns ? Have you seen Venus 

•11 1 • ,1 . Venus and the 

at mid-day, or can you recognize her in the evening, as moon 




Urania. 



38 A Study of the Sky. 

she glows with silvery sheen in the west, and weaves her 
way in and out among the stars, from night to night ? 
Can Venus be seen at midnight ? Is the full moon vis- 
ible at noon ? Do the horns of the crescent moon point 
toward the sun ? Does the moon always set directly in 
the west ? In what direction does the moon move 
among the stars, eastward or westward ? 
The Milky On some night when the sky was perfectly clear, and 

Way. ^g moon was n0 |- m sight, have you made a study of 

the wonderful river of light which foams across the sky ? 
Have you seen the dark rocks against which it dashes, 
the foaming eddies here and there, and the profusion of 
starry spray with which it besprinkles the adjoining con- 
stellations ? 

Must you give a negative answer to most of these 
questions ? Then let the arm-chair control you no 
longer. Yield to the charms of Urania : woo her, and 
make her your friend. How shall this wooing proceed ? 
This chapter and the next four shall be your guide in 
this matter. In them will be developed an orderly 
method of procedure, which will lead, by easy stages, 
to the attainment of the desired end. 

First we mention briefly the classes of objects with 
which our study will be concerned. 

The fixed stars, or more simply the stars, are those 
brilliant points of light which stud the heavens, remain- 
ing in the same relative position from year to year, and 
from century to century, as nearly as the unaided eye 
can judge. Had an ancient Assyrian made a rude rep- 
resentation of the Great Dipper on one of his tablets of 
clay, we should at this day instantly recognize the con- 
figuration as one with which we are familiar. The fixed 
stars are suns, at such amazing distances from us that 
their motions seem exceedingly small. 



The fixed stars. 



The Heavens and their Appare?it Revolution. 39 



The nebulae are cloud-like masses of matter of vast 
extent, which are as far away as the stars. The great 
nebula in Andromeda can be seen easily with the naked 
eye, and the nebula in the sword-handle of Orion can be 
glimpsed. The vast majority of these objects, however, 
are visible only with powerful telescopes. Quite a num- 
ber are invisible even in the largest instruments, but 
have imprinted themselves on photographic plates ex- 
posed for hours in the foci of special star-cameras. 

The planets look like the fixed stars, when viewed 
with the naked eye, except that they do not twinkle. 
Jupiter and Venus are usually brighter than the brightest 
fixed stars. Mars, Mercury, Saturn, Uranus, and Nep- 
tune are less brilliant, Neptune never being visible to 
the unaided eye. The ancients, who were unacquainted 
with Uranus and Neptune, discovered that the other 
planets changed their apparent positions among the 
stars. From this circumstance arose the designation 
'/planet," which signifies "wanderer.*' These bodies 
are all comparatively near us, the most distant being less 
than three thousand million miles away. The minor 
planets, also called asteroids, are small bodies coursing 
about the sun in paths which lie between those of Mars 
and Jupiter. 

Comets derive their name, which means ' ' hairy 
ones," from their tails or trains, which often attain to 
great magnificence. Some of them are to be regarded 
as members of the solar system, since they revolve about 
the sun in closed curves. Others are simply visitors, 
which display their beauty for a time, and then whisk 
off to regions unknown. 

Meteors are those rash little bodies which plunge 
headlong into the earth, and thus end their careers in an 
outburst of evanescent glory. 



The nebulae. 



The planets. 



Meteors. 



40 



A Study of the Sky. 



Sun, moon, and 
earth. 



The Great 
Dipper. 



The sun, moon, and earth need no particular mention, 

the earth being one of the sun's family of planets, and 

the moon being her attendant ; the moon belongs to the 

class of bodies known as satellites, which revolve 

about the planets. 

We are now in a position to understand any mention 
ocr. 




Fig. 9.— The Great Dipper. 

which may be made of these celestial objects, prior to 
the detailed discussion of them which will come later. 

Our present business is to get acquainted with the fixed 
stars. The Great Dipper is the first configuration to be 
learned (Fig. 9). Around the margin of the diagram are 
given dates, which will aid in finding it. To locate it on 
February 1 at 8 p. m. , the book is to be held out in front 



The Heavens and their Apparent Revolution. 4 



of the reader, with the center of the diagram on a level 

with his eyes, and the point marked February 1 at the 

uppermost part of the circle. The diagram then shows 

that the Dipper is at the right of Polaris, the pole-star. 

Two of the stars in the bowl are called the Pointers, 

because they point toward Polaris. The distance 

between the Pointers is about five degrees, and should 

be fixed in mind as a sort of yardstick with which to The yardstick. 

estimate distances between other stars. The distance 

from Polaris to the nearest Pointer is about five times 

our yardstick. 

In order to get an accurate notion of measurement by 
degrees, imagine that the stars are fastened upon the measurement. 
inner surface of a huge 
celestial sphere, the 
distance from the earth 
to the surface of the 
sphere being so great 
as to be beyond ade- 
quate comprehension 
(Fig. 10). Let E be 
the position of the ob- 
server on the earth, 
while S and S' are two 
stars said to be 30 
apart. Through these 

stars a circle whose center is at E is drawn on the sur- 
face of the celestial sphere. From E two lines, ES 
and ES', are drawn, making the angle SES'. This 
angle is measured by the number of degrees in the arc 
SS', there being 360 in an entire circle. If the arc 
SS' is one twelfth of the entire circumference, the angle 
SES' is an angle of 30 . 

Now the diameter of the earth, which is less than 




Fig. 10.— Measurement of an Angle. 



42 



A Study of the Sky. 



Center of the 
sphere. 



8,000 miles, is very minute in comparison with the 
distance from the earth to any fixed star, for the latter 
distance is expressed by many millions of millions of 
miles. In consequence of this, the angular distance 
between any two stars always appears the same, wher- 
ever the observer may be on our planet. 

If an astronomer in Boston were to measure the 
Boston and San angular distance between Polaris and one of the Pointers, 

Francisco. , 

with the most perfect instrument ever devised for such 
work, and another astronomer in San Francisco were to 
make a similar measurement, the two results would 
agree if the observations were free from error. This 
remark applies only to the fixed stars, and is not true 
of the moon or the planets, which are much nearer to us. 

For all our naked-eye observations we may therefore 
assume that the eye of the observer is located in the 
center of the celestial sphere, and that all of the fixed 
stars are fastened to the sphere, turning with it as it 
turns. We are thus taken back to the crystal spheres, 
studded with golden nails, with which the ancient 
Greeks dealt. We may imagine the moon, the planets, 
and comets to be likewise located on the inner surface 
of the sphere, but to be endowed with powers of loco- 
motion, so that they can move about among the golden 
nails. 

Remembering then that we are in the center of the 
celestial sphere, we ask the question, "How does the 
star-sphere appear to turn?" In answering this we 
have recourse to the cause of the apparent turning, 
which is the spinning of the earth upon its axis with 
such evenness of motion that we experience no jar or 
shock. 

Every reader has had similar experiences with motions 
on the earth's surface. A sleeping-car passenger awakes 



Rotation of the 
sphere. 



A sleeping car. 



The poles. 



The Heavens and their Apparent Revolution. 43 

suddenly in the middle of the night, and concludes 
by the comparative silence and the absence of noticeable 
jarring that his train is stopping at some station. Look- 
ing out of the window he sees a freight train apparently 
slowly backing on the next track. The truth is that the 
freight train is at rest, while his own train is just start- 
ing up. 

A passenger steamer leaves Chicago at night ; having A stea mer 
gotten fairly out of the harbor, it turns in order to head 
in a certain direction. While it is turning the lights of 
the city and the stars in the sky appear to the passen- 
gers to be revolving in the opposite direction to that in 
which they themselves are turning. 

Conceive the axis of the earth to be prolonged till 
it strikes the celestial sphere. The north end of the axis 
strikes near Polaris, at a point called the north celestial 
pole, The south end strikes at the opposite point of the 
celestial sphere, called the south celestial pole. A 
straight line joining these two points is the axis of the 
celestial sphere, about which it appears to rotate. If there 
were a bright star at each pole, and we could see both of 
them at the same time, we should have little difficulty in 
getting an accurate idea of just how the heavens rotate. 

A line drawn from the eye of the observer parallel to 
the earth's axis, and prolonged to the celestial sphere, 
would strike so near the centers of the stars, which 
we have imagined to be at the celestial poles, that no as- 
tronomer could measure the deviation. We are therefore 
entirely justified in laying down the following principle 
to guide our thinking in this matter of the apparent 
daily rotation of the star-sphere : 

The star-sphere appears to turn once a day about a?i 
axis drawn from the observer s eye to the ?wrth celestial 
pole, which is in the vicinity of Polaris. 



The axis of 
rotation. 



44 



A Study of the Sky. 



The north pole. 



Observations 
and records. 



The first draw- 
ing. 



Polaris and the 
Pointers. 



We may now locate the north celestial pole more ac- 
curately than by saying that it is in the vicinity of 
Polaris. The star which is situated at the bend of the 
handle of the Great Dipper is called Mizar. Let the 
eye travel slowly from Polaris directly toward Mizar ; 
when it has gone a distance equal to one fourth of the 
distance between the Pointers, it has reached the north 
celestial pole. 

But the explanation which has just been given does 
not suffice for our needs. The motion of rotation can 
be well grasped only by repeated observations of 
the heavens. Since we now purpose to get acquainted 
with the heavens, gaining knowledge which will be a 
source of delight throughout life, we must not only 
observe, but also record some of our observations, that 
they may be the better fixed in mind. A common 
blank book will answer our needs. 

A picture of the Great Dipper is first to be drawn. 
We get it and Polaris well in mind by looking at them 
a minute or two. Polaris is considerably brighter than 
any other star within fifteen degrees of it, and is almost 
directly north of us, about half way from the horizon to 
the zenith. It is also at the end of the handle of 
the Little Dipper, which is shown in the figure. The 
distance from Polaris to the furthest corner of the bowl 
of the Little Dipper is nearly twenty degrees, and 
the curved handle is about twelve degrees in length. 

We first locate Polaris on a page of the blank book, 
and then draw a faint line directly down from it, to rep- 
resent a vertical line ; we also draw a horizontal line 
similarly. These are only to assist in getting the Dip- 
per correctly located. The Pointers are next drawn, 
care being taken that the distance from Polaris to 
the nearest Pointer shall be five times the distance 



The Heavens and their Appai'ent Revolution. 45 

between the Pointers. Then come the other two stars 
of the bowl in their proper relative positions, and lastly 
the handle. After this the Little Dipper may be drawn. 

The picture now resembles Fig. n, except that the 
vertical and horizontal lines 

may not lie in the same posi- , • 

tions with reference to the stars V' 

as in the diagram, and that ••*•••»' 

the dotted lines have not been 
drawn. The date of obser- •— ■• 

vation and the time (within 
five minutes) when the drawing 
was finished are recorded. If 
the drawing was made early in 
the evening, another similar 
one should be made just before 

retiring for the night. Acorn- ,,»'• • 9 

parison of the two will show * \ J--'''" 

that the Dippers have shifted | 

their positions with reference 

to the vertical and horizontal Fig m _ The Twq DippERs 

lines. After watching the Dip- 
pers for two or three nights the answers to the following 
queries may be written down in the note-book : 

Is Polaris as bright as either of the Pointers ? Is any 
star in the bowl of the Little Dipper brighter than the Q ueries - 
faintest in the bowl of the Great Dipper ? How many 
stars can be seen within the bowl of the Great Dipper ? 
There is a faint star, called Alcor, which is within a 
degree of Mizar ; what is its color ? The distance 
from Alcor to Mizar is what fraction of a degree ? What 
is the color of each of the Pointers (white, yellowish, 
reddish, bluish)? Is the Great Dipper higher up late in 
the evening than early ? At some time during the night 



46 A Study of the Sky. 

would the bowl of the Great Dipper be near the zenith ? 
How the If so would the handle be east or west of the bowl 

Dipper moves. 

at that time ? At about what time on the day of obser- 
vation was the bowl underneath Polaris ? Where was the 
bowl of the Little Dipper with reference to Polaris, when 
the large bowl was underneath ? If a watch were held 
between your eye and Polaris in such a position that you 
looked squarely at its face, would the extremity of the 
minute hand travel around the face in the same direction 
in which the Dippers go around the pole-star, or in the 
opposite direction ? Twelve hours after the time of your 
first observation where would the Great Dipper be with 
reference to Polaris ? Does Mizar keep at the same dis- 
tance from Polaris ? Does the bowl of the Great Dipper 
ever disappear below your horizon ? Does this bowl 
move downward, when at the left of the pole-star as you 
face it ? If it were below Polaris would it appear to be 
moving toward your right as you face it ? Is there any 
time during the twenty-four hours which are consumed 
by a revolution of the star-sphere when Alcor appears 
to be exactly in line between Mizar and Polaris ? 
Motion of Did you ever see the moon close to either Dipper ? If 

you turn your back on the pole-star and face southward 
will a star off in the south appear to be traveling toward 
your right ? If you face westward and look up at a star 
near the zenith, will that star be moving westward down 
the vault of the sky ? Will its distance from Polaris ap- 
parently alter as the hours of the night roll on ? Will 
the star slide straight down the sky, as if endeavoring to 
reach the horizon by the shortest path, or will it veer off 
toward the north ? A star has just risen close by 
the east point of the horizon ; as it climbs the sky will it 
go straight toward the zenith, or will it veer off toward 
the south ? Are there any stars except Polaris and those 



other stars. 



The Heavens and their Apparent Revolution. 47 

in the Dippers which never disappear below your 
horizon ? 

If the reader is not sure about the answer to any 
of these queries, he should watch the heavens until 
doubt gives way to certainty. 

The expression "celestial sphere," which we have 

let-, , . , . The definition 

used so ireely, has a technical meaning among astrono- of the celestial 
mers. They define it as a sphere whose radius is in- 
finite, so that the remotest stars lie far within it. The 
apparent position of any object on this sphere is the 
point where a line drawn from the observer's eye 
through the object, and extended to an infinite distance, 
pierces the sphere. 

Our first and most difficult lesson in astronomy is at 
an end. 



sphere. 



CHAPTER III. 



THE CONSTELLATIONS IN GENERAL. 



' ' Look how the floor of heaven 
Is thick inlaid with patines of bright gold ; 
There's not the smallest orb which thou behold' st, 
But in his motion like an angel sings ; 
Still quiring to the young-eyed cherubins." 

— Shakespeare. 

Men of the earliest ages were quick to perceive that 
there were certain striking groups of stars, some of 
The menagerie, which rudely resembled men and animals. To these 
they gave names, according to their fancy. Even the 
most savage nations have not failed to name certain 
groups. A celestial globe of the present, day is covered 
with a veritable menagerie of monsters, the names of 
which are largely taken from Greek mythology. We 
cannot trace the origin of these names satisfactorily ; 
some of them occur in the most ancient writings. Many 
of the groupings are highly artificial, and were ap- 
parently devised to immortalize the heroes and heroines 
of mythological tales. 

The story of Andromeda is a case in point. She was 
a daughter of Cepheus, a king of the Ethiopians. Her 
mother, Cassiopeia, imprudently boasted that the beauty 
of Andromeda excelled that of the Nereids, who were 
lovely divinities inhabiting the depths of the Mediter- 
ranean. Incensed at this, the Nereids betook them- 
selves to Poseidon, the chief divinity of that sea, and 
prevailed upon him to visit Libya by an inundation, 



Andromeda. 



The Constellations in General. 49 

and further to send a sea-monster to ravage the unhappy 
land. An oracle promised deliverance if Andromeda 
were given up to the rapacious maw of the leviathan. 
The clamor of his people obliged Cepheus to yield, and 
Andromeda was chained to a rock. 

It so happened that a brave youth, Perseus by name, 
had just accomplished the daring feat of slaying Medusa, 
one of the Gorgons. Her snaky head, which turned 
the beholder to stone, was borne aloft by Perseus in 
triumph. From her blood sprang Pegasus, the winged 
horse. As Perseus journeyed homeward through the 
air, with his horrid trophy, he spied Andromeda. 
Everybody will admit that the only proper thing for this 
prehistoric knight to do was to kill Cetus, the sea- 
monster, break the chains of Andromeda, and marry 
her. He proved equal to all these demands, though 
her color did not match his. 

Among the stars we now find Andromeda, Cassiopeia, 
Cepheus, Cetus, Perseus with Medusa's head still in his 
hand, and Pegasus. 

The Great Dipper, to which we paid so much atten- 
tion in the last chapter, is a portion of the constellation 
of the Great Bear. One of the Greek legends is that 
Jupiter, who had a penchant for falling in love with fair 
women, wooed the nymph Callisto, and metamorphosed 
her into a bear, lest Juno should enliven his domestic 
affairs unduly. But Juno was not deceived by this ruse, 
and persuaded Diana to slay the bear. Jupiter then 
gave Juno a standing lesson about meddling with his 
royal prerogatives by placing Callisto among the stars, 
under the name of Arctos, the Greek word for bear. 

The Iroquois Indians, when America was discovered, 
are said to have called this star-group Okouari, which 
signifies bear. 



Perseus. 



The Great Bear. 



The Iroquois. 



5Q 



A Study of the Sky. 



The Chariot.' 



The ancient 
constellations. 



Christian 
heavens. 



Heraldic 
constellations. 



The zodiac. 



The Greeks also applied the designation ' ' The 
Chariot ' ' to the Great Dipper. The bowl may be con- 
sidered as the body of the chariot, and the handle as the 
pole. This conceit survives in England, where the 
appellation "King Charles' Wain" is used, and in 
France, where it is often called " David's Chariot." 

Ptolemy, who did so much in systematizing the 
astronomy of his day, has transmitted to us forty-eight 
constellations, which are now called the . " ancient con- 
stellations," and are accepted and retained largely on 
account of their historic interest. Their names are 
thoroughly woven into astronomical literature, both 
popular and scientific. 

Some attempts have been made to dispossess the 
ancient heroes of their happy hunting grounds. Early 
in the eighth century the Venerable Bede advocated a 
plan for Christianizing the heavens. Henceforth the 
apostles were to have conspicuous places in the sky. 
Peter was to take the place of the Ram, as was fitting, 
and the other disciples were to be distributed around 
the zodiac after him. 

In the seventeenth century Professor Weigel, of the 
University of Jena, proposed that a series of heraldic 
constellations be formed, the zodiac being composed of 
the arms of the twelve foremost families in Europe. 
But this attempt to displace the old scheme, as well as 
all others, failed. 

The zodiac, or zone of animals, is a belt sixteen 
degrees wide, which extends around the sky like the 
stripe on a croquet ball. From antiquity onward much 
attention has been paid to the constellations in it. 
Imagine that a line from the center of the sun to the 
earth's center is prolonged through the earth, and 
extended till it meets the celestial sphere. 



Other names. 



The Constellations in General. 51 

While the earth travels round the sun in its annual 
journey, the extremity of this line traces a circle on the 
celestial sphere. The name of the circle is ' 'the ecliptic. ' ' The ecliptic. 
To an eye situated at the sun's center the earth would 
appear to travel around the ecliptic. To an eye placed 
at the earth's center the sun would similarly appear to 
course along the ecliptic, taking a year to make the 
complete circuit, passing through the zodiacal constel- 
lations in succession. The ecliptic lies in the middle of 
the zodiac, which extends eight degrees each side of it. 
As we watch the sun, moon, and planets, they always 
appear to lie in the zodiac. 

The ancients gave to certain small and conspicuous 
groups special names, such as the Pleiades and the Hy- 
ades. Individual stars of pronounced brightness were 
also named. We glance for a moment at some interest- 
ing facts concerning the Pleiades. 

The Pleiades were often used in connection with 
the calendar by ancient peoples, and are still employed 
thus by some savage tribes. This group of stars is situ- 
ated near the ecliptic. The sun, therefore, in his annual 
journey, gets so near them at one time of the year that 
they cannot be seen for several days. Six months after 
this time, when the sun has gone half way round 
the heavens, it is opposite the Pleiades, so that they rise 
when it sets, and vice versa. From Hesiod we learn 
that the Greeks in his day accounted the winter season 
as commencing when the Pleiades were seen low down 
in the east soon after sunset, and the summer season 
when they set soon after the sun. 

The Society Islanders are said to have divided the The Society 
year into two parts, according to the position of the 
Pleiades. That half of the year during which they 
could be seen early in the evening was called ' ' the 



The Pleiades. 



Islanders. 



52 



A Study of the Sky. 



The Druids. 



The Peruvians. 



Australian 
savages. 



Pleiades above. ' ' The other half was ' ' the Pleiades 
below. ' ' 

The rising of the Pleiades at sunset occurs about No- 
vember i. On that night was one of the most note- 
worthy festivals of the Druids, in which they celebrated 
the destruction and rejuvenation of the world. The 
sacred fire, which had burned continuously in the temple 
during the past year, was extinguished, and then the 
spirits of those who had died during the year embarked 
in ghostly array in the boats which were to take them to 
the seat of judgment, where the god of the dead appor- 
tioned to each his lot. In the church calendar of to-day 
November i is known as All Saints' Day. The preced- 
ing evening is Hallowe'en. The following day is All 
Souls' Day, and is celebrated in the Roman Catholic 
Church by supplications for the souls of the pious dead. 

A festival commemorative of the dead is held at this 
time of year in many parts of the world. The Peruvi- 
ans visit the tombs of their relatives, to bring food 
and drink for the departed, and to lament with plaintive 
songs and weeping. In India the month of November 
is called the month of the Pleiades, and a Hindu festival 
of the dead is celebrated about the middle of the month. 
The Persians once named the month after the angel 
of death. 

Australian savages are said still to hold a 
boree " at this season, in honor of the Pleiades 
say they, " are very good to the black fellows." 
occasions are also festivals of the dead ; the 



corro- 

which, 

These 

savages 



paint white stripes upon their bodies in such fashion that 
they appear like skeletons, as they execute weird noc- 
turnal dances about their fires. 

From Prescott's " History of the Conquest of Mex- 
ico" we learn that the Mexicans celebrated a great 



The Constellatioyis in General. 53 

cycle of fifty-two years, the celebration occurring on 
a November night. There was a tradition that the The Mexicans, 
world was once destroyed at this time. When the 
shades of evening fell, and the Pleiades rose, the cere- 
monies began. As this group of stars approached the 
zenith a human sacrifice was offered, to avert a repeti- 
tion of the dreadful calamity. When once the Pleiades 
had passed the highest point of their course, and were 
seen to be descending in the west, the gloom and 
dismay of the people gave place to rejoicing. 

The names now used for most of the stars of the first 
magnitude come from Greek or Latin sources, and 

t>i /— Proper names 

are significant. Thus Arcturus comes from the Greek, of stars. 
and means " the bear-driver." Antares, the red star in 
the heart of the Scorpion, shows by its name that it 
is the rival of Ares (the Greek name for Mars, the ruddy 
planet). The word Sirius is probably derived from the 
Greek <7£ipto$ } and therefore signifies "the scorching 
one." Quite a number of names were given by the 
Arabians. Aldebaran signifies ' ' the follower " ; it is 
supposed to have received this designation because it 
rises shortly after the Pleiades. Altair, ' ' the flying 
eagle," is the brightest star in the constellation of 
Aquila, the Eagle. Betelgeuse is a modification of the 
Arabic Ibt-al-jauza, which means "the giant's shoul- 
der" ; the star is located in the shoulder of Orion, the 
mighty hunter. 

Stars which had no proper names were, up to the be- 
ginning of the seventeenth century, usually designated 
by referring to their positions in the constellations. 
Thus we read of the star in the right knee of Bootes, or 
in the club of Hercules. This inadequate plan is 
happily no longer in vogue. 

In 1603 Bayer published a star atlas in which he made 



54 



A Study of the Sky. 



The modern 
system of 
naming-. 



Flamsteed's 
numbers. 



Catalo°rues. 



use of the letters of the Greek and Roman alphabets. 
According to this system the brightest star in the 
constellation Lyra is called Alpha Lyrse.* The next 
star in that constellation, in point of brightness, is Beta 
Lyrae. When the letters of the Greek alphabet have 
been exhausted, and there remain stars yet unlettered, 
the Roman alphabet is taken up. 

If all the letters of the Roman alphabet have been 
used and there yet remain naked-eye stars which are 
unnamed, numbers assigned by the astronomer Flam- 
steed are employed. At present every star visible to the 
unassisted eye can be referred to by letter or number. 
The system of numbers is entirely independent of the 
letters, every star in a given constellation having a num- 
ber, even though it may have been previously called by 
a letter. The numbers were not given in order of 
brightness. When the daily revolution of the stars 
brought the constellation Taurus to the meridian of 
Greenwich, the first naked-eye star which crossed the 
meridian was called by Flamsteed i Tauri ; the next star 
was 2 Tauri, etc. 

The hundreds of thousands of faint stars whose posi- 
tions have been determined by modern astronomers 
receive their names from their current numbers in star 
catalogues. For instance the 1634th star in Lalande's 
catalogue is known as Lalande 1634. The stars in all 
modern catalogues are arranged in the order in which 
they cross the meridian of any place, without reference 
to the constellations within whose boundaries they lie. 

What does a modern catalogue tell about each star 
which it contains ? This question cannot well be 
answered until we learn the meanings of two simple ex- 



* Lyrcz is the genitive case, or, as we would say in English, the possessive 
case of the Latin word lyra. 



The Constellations in General. 55 

pressions, " right ascension " and "declination." These 

terms are analogous to those used in geography in ani^edfnaScm 

locating places on the earth. As there is a terrestrial 

equator, so there is a celestial equator, as heretofore 

explained. As the latitude of a city is its distance, 

expressed in degrees, from the terrestrial equator, so the 

declination of a star is its distance from the celestial 

equator. There is a prime meridian on the earth, e. g. , 

the meridian of Greenwich, from which longitude is 

reckoned eastward or westward ; there is also a certain 

celestial meridian which passes through the celestial 

poles, and cuts the celestial equator at a particular point 

called the "vernal equinox," the location of which we 

shall explain more particularly hereafter. As the city of 

Denver has a longitude of seven hours, so some star has 

a right ascension of seven hours. While longitude on 

the earth is reckoned either eastward or westward from 

the principal meridian, the right ascension of a star is 

reckoned eastward only. 

In a star catalogue we expect to find three things 
stated about each star, its right ascension, its declina- 
tion, and its brightness. An explanation of the method 
of estimating brightness will be given in the next chapter. 

The letters of the Greek alphabet are given below, for 
the benefit of those who may not know them. They will The Greek 
slip easily into the memory, in the process of learning the a p 
constellations which are given in the next three chapters. 



a 


Alpha. 


1 


Iota (io'ta). 


P 


Rho. 


P 


Beta (ba'ta). 


fc 


Kappa. 


(T 


Sigma. 


r 


Gamma. 


X 


Lambda. 


T 


Tau (tou). 


d 


Delta. 


V 


Mu (mii). 


U 


Upsilon 7 . 


£ 


Epsilon'. 


V 


Nu (nii). 


<P 


Phi (phe). 


£ 


Zeta (za'ta). 


£ 


Xi (kse). 


X 


Chi (ke). 


f\ 


Eta (a'ta). 





Omicron 7 . 


<P 


Psi (pse). 


e 


Theta (tha'ta). 


77 


Pi (pe). 


(.0 


Om&'ga. 



A review. 



CHAPTER IV. 

THE CONSTELLATIONS FOR JANUARY AND FEBRUARY. 

' ' Ye quenchless stars ! so eloquently bright, 
Untroubled sentries of the shadowy night, 
While half the world is lapp'd in downy dreams, 
And round the lattice creep your midnight beams, 
How sweet to gaze upon your placid eyes, 
In lambent beauty looking from the skies ! " 

— Montgomery. 

We are now ready to confront the sky for the purpose 
of getting a hailing acquaintance with the most interest- 
ing of the star-groups. For we have already learned 
something of their origin, of the methods of naming the 
stars in each constellation, and the way of locating them 
by right ascension and declination. We have also ob- 
tained ideas concerning the apparent daily motion of the 
star-sphere, and can therefore foresee, to a certain ex- 
tent, the effect of this motion on the position of a con- 
stellation during the successive hours of the night. 

Every reader will not find time to learn all the constel- 
lations described in this and the next two chapters. 
Three constei- ^ ut ever T one should form the acquaintance of at least 
lations a month, three constellations a month. Therefore the three most 
conspicuous constellations of those given for each month 
are named in black letter. One may read the remainder 
of the book before the constellation work is finished. 
The work is so arranged that it may be done, a little at 
a time, during the first six months of the year. During 
the vacation months of summer the pleasant evenings 

56 



The character- 
istic 
tion. 



The Constellations for January and February. 57 

will tempt the observer to review those constellations 
which are then visible, and thus to fasten them in the 
memory. 

Only those stars which form the characteristic con- 
figuration of each constellation are given in the illustra- jstic configura 
tion of it. Many other adjoining stars, which are 
generally fainter, are within the arbitrary boundaries of 
the constellation, as laid down on standard maps of the 
heavens. To these extra stars we pay no attention ; an 
attempt to learn them would be a waste of energy, as 
not even professional astronomers are familiar with them. 
It is not advisable to learn the Greek letter for every 
star. If any particular star interests the reader 
especially, it is well to remember its name. For 
example, Epsilon Lyrse is a famous quadruple star, 
which consists of two adjoining pairs of revolving suns, 
and is used as a test of acuteness of vision. It is best to 
learn the names of those bright stars which, like Sirius, 
Arcturus, and Vega, are among the most splendid 
objects in the sky. Such names are printed in the 
diagrams. 

The faintest star which can be seen by an average eye 
is said to be of the sixth magnitude. A star which is Stella 
two and one half times as bright as this, and can be 
seen easily, is of the fifth magnitude. A fourth magni- 
tude star is two and one half times as bright as one of 
the fifth. Thus the scale of magnitudes is ascended till 
we reach the first magnitude. Fewer than twenty of 
the fixed stars are bright enough to be rated as of the 
first magnitude, and some of them are much brighter 
than others. A standard first magnitude star is one 
hundred times as bright as one of the sixth magnitude. 
The magnitudes of the stars are indicated by the symbols 
given on the next page : 



magnitudes. 



58 



A Study of the Sky. 



Estimation of 
distance. 



Hints. 



Observation 
exercises. 



First magnitude, • 
Second magnitude, -•- 
Third magnitude, "f 
Fourth magnitude, -f- 
Fifth magnitude, • 

Two stars which appear in a diagram of the same 
magnitude may seem to the observer quite different. 
Both stars, for instance, may be given of the third mag- 
nitude, though one is only a little fainter than magnitude 
three and one half, while the other is nearly as bright as 
magnitude two and one half. For small distances the 
observer may use as a measuring rod the distance be- 
tween the Pointers, which is close to 5 . For longer 
distances it will be convenient to remember that the 
distance from the extremity of the handle of the Great 
Dipper to the Pointer at the top of the Dipper bowl 
is 26 . 

In learning a constellation one should first familiarize 
himself with the illustration given in the book, studying 
it till he can make a rude sketch, showing the relative 
positions of the stars. Having this mental picture, he 
can face the sky with a good degree of assurance, and will 
generally have little difficulty in picking out the stars 
desired. The constellations will not usually appear the 
same side up as in the book. But if the observer 
imagines a line drawn on the sky from the north pole, 
or practically from Polaris, directly toward the desired 
constellation and through its center, this line will run 
from the center of the upper edge of the diagram to the 
center of the lower edge. 

After the description of each constellation are given a 
few queries, the answers to which may be written in the 
observer's note-book. If two or more persons observe 



The Constellations for January and February. 59 



together, the work will prove quite fascinating. But in 
answering the queries one should never allow his judg- independence, 
ment to be swayed by that of a companion. The eyes 
of one person are not like those of another, and each 
should put down what his own eyes reveal. 
Ursa Major. 
The Great Dipper, with which we have already be- 
come familiar, is a portion of Ursa Major, the Great Bear. 






,+. 



> 






k-*> 



Te if*- 



i 



Fig. 12.— Ursa Major. 

About 9 p. m. during any evening in January this 
constellation is found at the right of Polaris. The Bear 
appears at that time to be balancing himself upon the 
tip of his tail. The star o (Fig. 12) marks the tip of the 
creature's nose. The animal is short one fore leg, but 
map-makers are accustomed to supply the missing mem- 
ber, despite the absence of available stars. Each of the 
three existing feet is marked by a couple of stars ; the 



Description. 



6o 



A Study of the Sky. 



The Bear's tail. 



The Dipper. 



Mizar. 



components of each pair are less than two degrees apart. 
i and ic mark the front foot ; A and fi mark the forward 
hind foot. The remaining hind foot is located by v and 
£. These three pairs of stars lie almost in a line, the 
central pair being about twenty degrees from each of 
the others. 

The handle of the Dipper is the tail of the Bear, and 
is of appropriate length for a cow. This anomaly, we 
are told by an old writer, is due to the fact that Jupiter 
lifted the bear by its tail, when he raised it to the sky. 

The stars in the Dipper have received proper names, 
which are sometimes used even by astronomers, who, 
except in the case of the stars of the first magnitude, 
usually prefer the Greek letter nomenclature, a Ursse 
Majoris is Dubhe ; ft is Merak ; y is Phecda ; d is Me- 
grez ; e is Alioth ; C is Mizar ; 77 is Benetnasch or Alkaid. 

Mizar is one of the finest of double stars, as seen with 
a small telescope, and was the first of such objects 
which the telescope revealed ; it was discovered in 1650, 
soon after the invention of that instrument. These two 
magnificent suns, one of the second, the other of the 
fourth magnitude, are slowly revolving about their com- 
mon center of gravity. The time of a complete revolu- 
tion is roughly estimated at 20,000 years. In 1889 
Prof. E. C. Pickering* discovered by means of observa- 
tions with the spectroscope that the brighter of the two 
components of Mizar is itself a double. The two stars 
composing it are thought to make one revolution about 
one another in one hundred and four days, the diameter 
of their orbit being about 140 million miles. The mass 
of the system is forty times that of the sun. Near 
Mizar is the faint star Alcor, which the average eye 
should see without difficulty. 

* Director of the Harvard College Observatory. 



Queries. 



The Constellations for Jaiiuary and Febrziary . 61 

According to mythology, Ursa Major is the nymph 
Callisto, who was so pleasing in Jupiter's eyes that Juno Mythology. 
became jealous. One version of the legend is that 
Jupiter changed Callisto to a bear, to avoid Juno's 
jealousy ; another version is that Juno took revenge 
upon her rival by changing her into a bear. Being un- 
willing to lose his favorite in this way, Jupiter trans- 
ported her to the stars. 

What is the magnitude of Alcor, and its distance 
(fraction of a degree) from Mizar ? Which is the 
brightest star in the Dipper ? How many stars are vis- 
ible within the bowl of the Dipper ? Twelve hours after 
the time of sketching the constellation, what is its 
position ? 

Ursa Minor. \ 

At 7 p. m., on any evening early in January, the 
Little Bear is suspended by his tail, the end of which is 
fastened at Polaris (Fig. 13). It has been suggested 
that the inordinate length of his tail is an illustration of 
the Darwinian law of adap- 
tation to environment, the "Polaris 
tail having been stretched 
in the process of swinging -^- 

the Bear around once in ^ * 
every twenty-four hours, -j^ 

for hundreds of years. & * 1^^. # 

This star-group is com- £f ^ 

monly called the Little ^~ .. _ ^^ 

Dipper ; the handle of the Y y> 

utensil is a neat curve con- 

... , Fig. 13. — Ursa Minor. 

taming tour stars, including 

the one by which it is joined to the bowl. The two The Little 
brightest stars in the bowl are called the ' ' Guardians of Dipper - 
the Pole. ' ' The constellation guided the Phenicians in 



Description. 



62 



A Study of the Sky. 



The north 
celestial pole. 



their voyages on the Mediterranean, just as the pole-star 
now affords to a seaman a method of checking the in- 
dications of his compass, should he fear that it is awry. 

Polaris is one of the nearest of our neighbors among 
Polaris. the fixed stars. Yet a railway train, speeding continu- 

ously at the rate of sixty miles an hour, would require 
600 millions of years to reach it. So enormous a 
distance is very difficult to measure, and is subject 
to considerable uncertainty arising from the unavoidable 
errors inherent in even the most careful measurements 
of experienced astronomers. 

The north pole of the heavens lies on a line from Po- 
laris to Mizar, being a little more than a degree from the 
former. Polaris has not always been the pole-star. 
Because of the attractions of the sun and moon upon the 
equatorial protuberance of the earth, the direction in 
which the axis of the earth points is continually chang- 
ing. The result is that the north celestial pole moves 
in a circle on the surface of the sphere. One revolution 
is made in 25,800 years. The circle passes near Vega, 
in the constellation of the Lyre, its center appearing to 
lie about half way from Polaris to Vega, not quite on 
a line joining them. Twelve thousand years hence Vega 
will be the pole-star, unless some unforeseen catas- 
trophe gives an unexpected shift to the earth's axis. 

Polaris is a double star, having a companion of mag- 
nitude 9.5, which can be detected with a telescope 
of two or three inches' aperture. By the ' ' aperture' ' of 
a telescope is meant the diameter of the object-glass, 
which is the lens at the large end of the telescope. 
Cassiopeia. 

The pole-star is midway between the Great Dipper 

Description. and a striking group of five stars, three of which are of 

the second magnitude, the other two being of the third. 



A double star. 



The Constellations for January and February . 63 

The group resembles a dilapidated W, and consists of ^dilapidated 
the stars /?, a, y, <5, e, shown in Fig. 14. By adding fc 
the figure is brought to a rude likeness to a broken- 
backed chair, y and fc forming the seat of the chair, 
while o and £ outline its back. 

Cassiopeia is often called "The Lady in the Chair," 
and one is thus 

led to suppose >^ ifc-#* 

that she is seated Tn / ^ 

ON / n x 

in the chair. But N / V N 

the map-makers x v^ _-A_y ~9~ p 

have ordered t£ \ /' 

otherwise, and _^_ / 

the queen dis- H ^-/? 

dains to sit on 

.1 • Fig. 14.— Cassiopeia. 

anything more * 

substantial than the ether. /?, a, y, and A; form her 

body; d lies in her knee, and : marks her foot. Her th?chair d " in 

hands are upraised, as if in prayer to the gods to spare 

her beautiful daughter Andromeda, the story of whose 

danger and rescue has already been told. 

Less than two degrees from fc, on the opposite 
side of it from y, appeared in November, 1572, a 
new star, which was bright enough to be seen in full 
sunshine. Tycho perceived it while out for an evening 
stroll, and thenceforth observed its changes assiduously. 
In December its fires paled perceptibly, and after a 
lapse of sixteen months it became invisible to the naked 
eye. When it first appeared it inspired great terror 
among the ignorant, and was thought to presage the 
end of the world. 

An opera-glass reveals many beautiful regions in Cas- 
siopeia, where the stars besprinkle the sky like diamond 
dust. A line drawn from fc to /?, and prolonged half as 



Tvcho's star. 



Clusters. 



6 4 



A Study of the Sky. 



Double star. 



Queries. 



Description. 



far again, terminates at a cluster of small stars discov- 
ered by Caroline Herschel, the sister and assistant of Sir 
William Herschel. A degree from d another fine field 
of stars is located. Any one who has a small telescope 
may spend considerable time pleasurably, exploring the 
Milky Way in and adjacent to Cassiopeia. 

Between a and y lies r h a star of the fourth magni- 
tude, which is comparatively near us, its light taking 
not much over twenty years to come to us. It has a 
colored companion too close to it to be detected without 
a telescope. The hue vies with that of the chameleon, 
having been called by various astronomers green, 
purple, blue, red, and lilac. Such a diversity is best ex- 
plained by changes in the star itself, though such 
changes seem improbable. 

Is rj in a direct line between a and y ? How many 
stars are at the end of a line drawn from ft through 
the middle point between a and r h and prolonged nearly 
an equal distance ? If ft is now at the left of the pole, 
and as high above the horizon as Polaris, will it be lower 
two hours hence, or higher ? 

Pegasus. 

Pegasus, the winged horse, is a very large constella- 
tion, the conspicuous portion of which is a large square, 
whose sides average 15 in length (Fig. 15). Three of 
the four stars in the square are of the second magnitude. 
One corner of the square lies at the extremity of a line 
drawn from Polaris to ft Cassiopeiae, and prolonged an 
equal distance beyond ft. The star at this corner is 
common to the two figures of Pegasus and Andromeda, 
and is universally called a Andromedae. The same line 
prolonged 14 further meets y, which is at another 
corner of the square. The square lies west of the zenith, 
about half way down to the horizon, at 7 p. m. in the 



The Constellations for Jaiiuary and February. 65 



middle of January, its uppermost side being the one just 
described. The square is the body of the horse, which The square, 
has no hind quarters. At the opposite corner of the 
square from a Andromedae lies a Pegasi. A line from 
the first of these stars to the second, prolonged an equal 
distance, passes ,^r 

1 a r' 



through Z 
neck, and 
nates at 0, 
is at the 
the head, 
the nose. 



in the 
termi- 
which 
top of 
e is in 
The 



gflndrvmedat. 



Vv 



two fore legs 
:start at /3, and 
are marked by 
dotted lines in 
the diagram. 
A line from 



M- 



,+< 



Jfrj 



yjr 



..'> 



>*" 



Fig. 15. 



Pegasus. 

to e, prolonged a little more than half its length, reaches 
a globular cluster, which can be seen with a good opera- 
glass, and is one of the finest condensed clusters in the 
sky. Star crowds upon star, and the center of the clus- 
ter is a blaze of glory, which seems to defy separation 
into individual stars. We have here a system of 
thousands of suns, each of which undoubtedly moves 
under the attraction of all the others. The cluster is at 
least one hundred millions of millions of miles away. 

When Perseus had killed the Gorgon Medusa, Pega- 
sus, the winged horse, sprung from her blood. Rising 
to the abodes of the immortals he became Jupiter's 
charger for a time. When Bellerophon wished to slay 
the Chimaera, it was necessary for him to bestride Pega- 
sus. Minerva gave him a golden bridle, with which he 
•caught the horse as he was drinking at the well Pirene. 



A star cluster. 



Mythology, 



Queries. 



Description. 



66 A Study of the Sky. 

The Chimaera vanquished, Bellerophon attempted to as- 
cend to heaven on the back of his winged steed. But 
Jupiter sent a gad-fly, which stung the animal and 
caused him to throw his rider. Pegasus then flew on to 
the stars. 

How many stars can you count on a moonless night, 
within the boundaries of the square ? Is - double to the 
naked eye ? Does the square set at the west point of 
the horizon, or north of that point? Which is the 
shortest side of the square ? 

Aquarius. 

Aquarius is low in the west in January, in the evening, 
and should be looked for as soon as the sky has become 
fairly dark.* A line from /S Pegasi to C Pegasi, when 

7 +-~i x 4 



v * x *~ 

*> T — ** 



Fig. i6. — Aquarius. 

prolonged two thirds of its length, reaches an equilateral 
triangle, composed of three stars of the third, fourth, 
and fifth magnitudes respectively, in the center of which 
lies a third magnitude star. The sides of the triangle are 
3° long: the four stars resemble a Y (Fig. 16). This is 

* Should the reader fail to get hold of this constellation because it is low in 
the west, further study of it may be postponed until early summer, when it is 
seen in the east, late in the evening. 



The Constellations for January and February \ 67 



the water-jar of Aquarius; from it flows a stream, which 
winds its way southward and eastward into the mouth of 
the Southern Fish, where lies the first magnitude star 
Fomalhaut (Fo-ma-lo). The stars -, r h y } and C form the 

Y or water-jar. The stream flowing down to Fomalhaut Fomalhaut. 
follows the dotted line in the diagram through <p, </', etc. 

The line is marked by several groups of faint stars, near 
<p, a, etc. /? Pegasi lies nearly midway between Polaris 
and Fomalhaut. At the right of the Y lies a rude 
short-handled dipper, which the observer will fail to find 
unless he looks very early in the evening, and as near 
the first of the month as practicable. Most of the stars 
which stand guard between the dipper and the stream, 
that the fish be not defrauded of the water, belong to 
the constellation. Lines joining the brighter ones of 
them form a configuration not unlike the outline of 
South America ; c 2 is at Cape Horn, the continent 
touching the stream at this point. C in the center of the 

Y lies close to the celestial equator, and therefore sets 
very near the west point of the horizon. 

There is a remarkable nebula situated i° from v 
toward e, which, in a large telescope, exhibits a resem- nebula." 
blance to the planet Saturn. It appears to be a world 
or system of worlds in formation. Should it, in the ages 
to come, become a gigantic Saturn-like form, having a 
central globe, surrounded by a thin flat ring composed 
of a myriad of smaller worlds, how magnificent and awe- 
inspiring a spectacle ! 

Aquarius is thought by some to represent the youth Mvtholo 
Ganymede, the most beautiful of mortals, whom Jupiter 
snatched to Mount Olympus to be his cup-bearer. 
With a fine appreciation of the distress of the bereaved 
parents he endeavored to assuage their grief by a 
present of a team of fine horses ! 



68 A Study of the Sky. 

How many faint stars can be seen close to </> ? Are 

Queries. there five groups of faint stars (from two to four stars in 

a group) lying in the stream, between y and Fomalhaut? 

When the water-jar is nearly setting in the west, what 

two stars in it lie most nearly in a horizontal line ? 

Pisces. 

Like Aquarius, this constellation is largely composed 

Description. of faint stars, the brightest one being of only the third 

magnitude. But the group lies in a dull region of the 



** 



#•"* 1 i 

Fig. 17.— Pisces. 

sky, so that the ribbon joining the two fishes can be 
readily traced (Fig. 17). The southernmost fish is com- 
The circlet. posed of a circlet of seven stars, 5 or 6° in diameter. 
Three of these stars, y, t, and A, are of the fourth mag- 
nitude ; the distance from 1 to I is 4 . y is 6° from each 
of the other stars. The center of the circlet lies 12 
south of the southern side of the square of Pegasus ; 1 is 
equidistant from a Pegasi and y Pegasi. From 1 in the 
circlet a row of stars runs eastward to a, a distance of 



The Constellatio7is for January and Febrziary. 69 

35 , and is a portion of the ribbon joining the two fish. 
a is called El Rischa, the Knot, and lies io° west of the 
western side of a well-marked, five-sided polygon, the 
average length of one side of which is 5 . The polygon, 
as we shall learn hereafter, is the head of Cetus, the sea- 
monster. At the Knot the ribbon turns at a sharp 
angle, and runs northwesterly a distance of 30 , ter- 
minating in a coarse group of faint stars, which may be 
found by prolonging a line from /? Pegasi to a Androm- 
edae eastward 15 , a little more than its own length. 

The vernal equinox, which is the point in the sky at The ver nai 
which the sun's center appears to lie, when it crosses e< * ulnox - 
the celestial equator in March, and ushers in the spring, 
lies in a barren spot of sky just east of the circlet of stars 
forming one fish. A line from y to I, extended as far 
again, ends at the equinox. 

FEBRUARY CONSTELLATIONS. 
Andromeda. 

This constellation is found early in the evening in the Descri tion 
northwest, a has already been mentioned as one corner 
of the square of Pegasus ; it is located by drawing a line 
from Polaris to /? Cassiopeiae, and prolonging it an equal 
distance. A line from Polaris to the middle point be- 
tween e Cassiopeia? and t of the same constellation, pro- 
longed an equal distance, ends at y (Fig. 18). The 
bright stars y5 and d lie nearly in line between a and y ; 
these four form one side of the maiden's form, a being 
in the head and y in one foot. /? is in her waist and d 
at one shoulder. Her outstretched arms run from - to 
^, and from d to y]. 

A line from /? across her waist to /j., when prolonged The gre at 
an equal distance, ends at the great nebula, which is nebula - 
plain to the naked eye. Here is a storehouse of un- 



7o 



A Study of the Sky. 



A double star. 



Queries. 



Description. 



created worlds, which is vast beyond all human compre- 
hension. The entire solar system, if flung into this 
mighty abyss of chaotic matter, would be as a few 



4* 



% 






-¥« 



M 



grains of sand in a 
wagon-load. 

Y is a fine double 
star, as seen with a 
small telescope, the 
components being 
of widely different 
hues, the smaller 
one being of the 
fifth magnitude ; a 
large telescope splits 
the small star in 
two, showing that 
it is composed of 
two revolving suns. 
The mythological 

story of Andromeda has been told at length already, 

and is therefore omitted here. 

What is the color of y ? Which is the brighter, ,3 or y ? 

Is the great nebula round or oval to the naked eye ? 

Aries. 

Aries lies in the northwest early in the evening in 
February. A line from Polaris to y Andromedse, when 
prolonged nearly 20 , terminates at a, the brightest star 
in the small triangle composed of a, /?, and y (Fig. 19). 
The distance from a to y is only 5 . The entire triangle 
is located in the head of the Ram. East of this triangle, 
between it and the Pleiades, are scattered a number 
of faint stars, which are sprinkled quite at random over 
the Ram's bodv. 



Fig. 18. — Andromeda. 



The Constellations for January and February. 71 

According to Grecian mythology a ram with a golden Mythology. 

-^- fleece, the gift of Mercury, 

\\ flew with two children, Helle 

x n and Phrixus, over a sea. Helle 

\ \ was so unfortunate as to drop 

off into the sea, which was 



\ Ml; accordingly named the Helles- 

\ J pont (the sea of Helle). The 

\ ' famous Argonautic expedition 

Y^y was ^ or tne recover y of the 
golden fleece. 

Fig. 19. — Aries. ° 

Cetus. 

Cetus should be studied early in February, and as 
soon as it is dark, for the constellation is then in the 
southwest, and sets early. The monster resembles a 
walrus ; his head 
alone is above the i--^-.. _ 
celestial equator. 

The body of T---^V 
the leviathan is -^ 

marked by a kite- % -w. 

shaped figure 

formed of the \ w 

stars /?, v], 6, C, &"" ' *">r 

and r (Fig. 20). \ 

/? lies on a line M~" m ...._ \ 

from Polaris y "^ -+;* y 

through C An- 
dromeda (which FlG - 20 --Cetus. 

is in one of the lady's arms), and is nearly 45 ° beyond Descripti 
the latter. The kite is 20 long from /3 to C. The tip 
of the tail of Cetus lies at 1, u° northwest of % The 
position of the pentagon forming the head («, y, etc.) is 
shown in the diagram, C being equi-distant from /9 and y, 



72 



A Study of the Sky. 



Mira. 



Mythology. 



Queries. 



Description. 



Pleiades and 
Hyades. 



but not directly in line with them. u marks the ex- 
tremity of a flipper. A line from a to y, when extended 
io° further westward, nearly strikes a Piscium. 

A little more than half way from C to y lies <>. This 
star has received the proper name Mira, the Wonderful, 
because of the remarkable changes of its brightness. It 
is visible to the naked eye only three months in a year ; 
on one occasion in the eighteenth century it became 
as bright as a first magnitude star, r is one of the most 
rapidly moving stars known. It is traveling across the 
kite toward rj, which it will reach in 19,000 years, if it 
keeps on at a uniform rate. 

Cetus is the sea-monster, frequently called ' ' the 
Whale," that was to devour Andromeda, by order of 
Neptune. But Perseus intercepted and killed him. 

Which is the brighter, a or /9 ? Does the naked eye 
show that u consists of more than one star? Less 
than half a degree from C lies a star of the fifth mag- 
nitude ; does it lie within the kite ? 
Taurus. 

Taurus, the Bull, is noteworthy because it contains 
the Pleiades, the Hyades, and the first magnitude star 
Aldebaran. It resembles Pegasus, in that only its head 
and fore shoulders have reached the sky. Nevertheless 
it makes a brave show of charging at Orion, the mighty 
hunter, of whom we have still to learn. 

The Pleiades are readily recognized. They are 25 ° 
east of a Arietis. Ten degrees east of the Pleiades, and 
less than that distance south is a V-shaped figure, 
which constitutes the face of the Bull, and contains 
Aldebaran. The horns are between 15 and 20 long, 
their tips being ft and C (Fig. 21). The V-shaped 
group is called the Hyades. Both the Pleiades and the 
Hyades should be examined with an opera-glass, as 



The Constellations for January and February \ 73 

they contain many stars, which are thus brought out 

well. Six of the Pleiades should reveal themselves to 

the unaided eye. On a good night, when the moon 

is below the horizon, a dozen stars may be seen by 

an acute eye. Alcyone, the brightest of the Pleiades, Alcyone. 

was once surmised to be the center of the universe, but 

the theory had no sufficient foundation and was soon 

abandoned. Photography has shown that shreds of 



^S 



rf/c/ebaro/i " 



* 






** 



Fig. 21. — Taurus. 

nebulosity cling to many of the Pleiades, as if they were 
the remnants of an original nebula from which the 
cluster has been evolved. 

In the eye of the Bull glows «, which is usually called 
by its Arabic name Aldebaran. Its distance from us, 
according to some of the latest measures, is about 100 
millions of millions of miles. 

Taurus, in common with the majority of the constella- 
tions of the zodiac, is one of the ancient Egyptian star- 



Aldebaran. 



Mythology. 



74 



A Study of the Sky 



Queries. 



Description. 



groups, and was associated with the bull Apis. The 
Greeks described it as a mild and milk-white bull, into 
which Jupiter changed himself when he wished to seek 
the favor of beautiful Europa. The Pleiades were seven 
in number, being the daughters of Atlas, and sisters 
of the Hyades ; one fell in love with a mortal, and 
hid herself from shame. When Atlas had joined the 
other Titans in an attack upon Jupiter, and had been 
conquered, he was condemned to uphold the sky. His 
sad fate led the Pleiades to make way with themselves. 
Both Atlas and Pleione, the father and mother, were 
placed in the sky in the same group with their devoted 
children. 

What is the color of Aldebaran ? What star in 
the V is double to the naked eye ? Is any one of the 
Pleiades double, as seen with an opera-glass ? 
Orion. 

One who can look upon this magnificent constellation 
without a thrill of delight has no eye for the beauties of 
the heavens. At 8 p. m. in the middle of February it is 
on the meridian in the south, half way from the horizon 
to the zenith. It resembles the figure of the mighty 
hunter, who stands facing us (Fig. 22); with his right 
hand he brandishes a club, with which he is about to 
smite charging Taurus full in the face. The top of the 
club is marked by two stars of the fifth magnitude, 2^° 
apart, which point nearly at C Tauri, which is 5 west of 
them, at the top of one of the Bull's horns. The belt of 
the giant is marked by the three second magnitude stars 
d, e, and C. The length of the belt, which is often called 
the Ell and Yard, is 3 ; it points westward toward the 
Pleiades, and eastward toward Sirius, the brightest of 
the fixed stars. On either side of the belt, at distances 
of about io°, lie Betelgeuse in the right shoulder, 



The Constellations for January arid February \ 75 



and Rigel in the left foot. These are respectively a and 
,3. In the left shoulder is y, also called Bellatrix, and in 
the right knee is n. The head is marked by a small 



*> ?r 



• V 



The sword. 



i; 



isosceles right tri- 
angle. Over the 
left arm is thrown 
the skin of a lion. 
From the belt dan- # 
gles a sword, . 
which consists of 
the third magni- 
tude star c,and two 
faint stars immedi- 
ately above it ; a 
good eye sees in 
the sword four 
faint stars, in a 
row. The first star 
above t is 0, which 
is involved in the 
great nebula of 
Orion. It has a 
hazy appearance 
to the naked eye. 

The celestial 
equator passes nearly through d, the uppermost star in 
the belt. 

Betelgeuse and Rigel must be bodies of amazing mag- BeteIgeuse 
nitude, for they are so far away that astronomers have and Ri s eL 
not been able to measure their distances ; yet they 
are among the brightest of the stars. It is safe to 
say that their distances exceed 200 million million miles. 

The great nebula, which is situated in the sword, ^ 

. . ' The great 

is the most marvelous object of its kind in the entire nebula. 



• 


X 










\ 1 


/ ^ 


V 

•a 




Fig. 22. 


— Orion. 



7 6 



A Study of the Sky. 



Mythology 



Queries. 



Description. 



sky. Even an opera-glass reveals a little of the central 
portion of it ; in a large telescope its magnificence 
bafBes description. In viewing it with a large telescope 
it is well to point the telescope just west of the nebula, 
and allow it to drift through the field of view. 0, which 
is involved in the nebula, is a sextuple star ; the four 
brightest stars in it have received the name of the 
Trapezium. 

The Milky Way runs hard by Orion, and has appar- 
ently besprinkled it with a shower of starry spray. The 
entire constellation, seen through an opera-glass, is well 
spangled with faint stars. 

Orion was a handsome giant and great hunter ; 
he led an unhappy life, on account of his beauty and 
accomplishments. He lost his eyesight in consequence 
of his first love affair ; after he recovered it by looking 
full at the rising sun, Aurora, the goddess of the dawn, 
fell in love with him and carried him off. According to 
another account no less a personage than Diana, whose 
heart was supposed to be Cupid proof, became en- 
amored of him. Her indignant brother Apollo took 
occasion one fine day to tease her about her skill in 
archery, and asserted that she could not hit a certain 
shining mark, which bobbed on a distant wave. She 
hit it, and lo ! it was Orion's head. 

What is the color of Betelgeuse ? What is the color 
of Rigel ? Does the middle star in the belt lie above or 
below a line connecting the other two ? Are there two 
stars, or three, in a line a degree south of the belt, and 
parallel to it, the line being as long as the belt ? 

Auriga. 

A little less than half way from Bellatrix (j Orionis) 
to Polaris is Capella, a first magnitude star, which is the 



The Constellations for Ja?iuary and February : 77 

leading luminary of Auriga. It is at one corner of an ir- 
regular five-sided figure, the other corners being at /?, /5 
Tauri, 0, and 1 (Fig. 23). The distance from Capella 
to /3 Tauri is 20 . The remainder of the constellation 
consists chiefly of inconspicuous stars, lying on the 
north and east sides of the five-sided polygon. Auriga 
signifies "the charioteer." A line from to /?, pro- "The" 

& . •■ > r charioteer. 

longed northward an equal distance, meets the fourth 
magnitude star d } which is ~ 

in the man's head. His ^_ a O. 

feet are at t and /? Tauri. , " "^ Cc Petfa 

Near Capella is a little tri- / \ -jh £ 

angle of fourth magnitude ' u 1 

stars ; two sides of it are / ?/ * £ 

3 long, and the third side W & \ 

only i°. One vertex of \ \ 

the triangle is in a line from \ \ 

Capella to c The triangle \ 1^ 

represents a kid, which the \ ,/f ^ 

charioteer carries in his v ' 

arms. ^ „ \ / 

Capella is comparatively «*/y~#- 

near us. According to the FlG " 2 3--Auriga. 

measures of one of the highest authorities* its distance 
is 170 millions of millions of miles. Light occupies 
twenty-nine years in traversing this abyss. Were it as 
close as our sun, it would be sixty times as bright as 
he is. 

About half way from to /5 Tauri lies a fine compact 
cluster of small stars, which may be picked up with an 
opera-glass, in which it looks like a star enveloped in a 
cloud mantle. 

Near ,3 Tauri, on a line between it and ,3 there 

* Dr. W. L. Elkin, of Yale College. 



Capella. 



A cluster. 



78 



A Study of the Sky. 



appeared in December, 1891, a new star. Professional 
Nova Auriga, astronomers, who usually have their eyes glued to the 
eyepieces of their telescopes, when observing, failed to 
see it. It was discovered late in January, 1892, by 
Dr. T. D. Anderson, a Scotch amateur. Its image 
was afterward found on photographic plates taken in 
December at the Harvard College Observatory. At the 
end of April it could scarcely be seen with the Lick 
36-inch glass. But in the following August it was 
bright enough for a three-inch telescope, and had ap- 
parently turned into a nebula. A fuller history of the 
wonderful object and the theories of astronomers about 
it will be given later. 
Mythology. The mythological history of this constellation is very 

obscure. Perhaps the charioteer may be best regarded 
as Phaeton, the ambitious youth who requested his 
father Helios (the sun) to let him drive his chariot 
across the sky for one day. The horses ran away and 
came so near the earth that it was nearly set on fire. A 
thunderbolt from Jupiter, who occasionally did a sensible 
thing, ended the young man's career. 
Queries. What is the color of Capella? Is Capella brighter 

than Betelgeuse ? 



Description. 



CHAPTER V. 

THE CONSTELLATIONS FOR MARCH AND APRIL. 

" Starry crowns of heaven, 
Set in azure night ! 
Linger yet a little 
Ere you hide your light." 

— Procter. 

Gemini. 

A line from Mizar (£ Ursse Majoris) carried down 
the handle of the Dipper and diagonally across the bowl 
to the two stars which lie in the front foot of the Bear, 
when prolonged 25 °, ends near Castor and Pollux. 
They are the brightest stars in Gemini, and are respect- 
ively designated by the letters « and /? (Fig. 24). Half 
way between Castor and the head of Orion is /j.. Some- 
what more than half way from Pollux to Betelgeuse is y. 
a, /5, y, and /i are the four corners of a box-like figure 
resembling an end view of an upright piano. The key- 
board projects from C to A, and the pedals lie between y 
and £. >?, which is 2^° west of /-/., is a variable, rang- 
ing from the third to the fourth magnitude. It is on a 
line from ;j. to C Tauri, at the top of one horn of the 
Bull. The heads of the twins contain Castor and Pollux 
respectively, y and /x mark their feet. 

The summer solstice, which is the point where the 

. . - , 1 p 1 The summer 

sun appears to be, when it is larthest north 01 the solstice, 
equator on June 21, is 2 west and a little north of r h 
close by a star of the fifth magnitude. 

Castor is one of the finest double stars in the heavens ; 

79 



8o 



A Study of the Sky 



Castor and 
Pollux. 



so bright are its two components that both can be 
readily seen in daytime with a ten-inch telescope. 
Nearly one thousand years are consumed by one revo- 
lution of this majestic pair. Castor is approaching us at 
the rate of eighteen miles a second, while Pollux keeps 
almost at the same distance from us. 

A little over one fourth of the way from ;j. to /S Tauri 

a 



0J 



v 



* 



Mythology. 



>-* 



/> r - 



\ 






Fig. 24. — Gemii 



is a splendid cluster, just visible to the naked eye. It is 
composed of hundreds of faint stars, and is roughly 
circular in form. The apparent diameter of the circle is 
two thirds that of the full moon. 

The brothers Castor and Pollux were two mythologi- 
cal knights, whose chief deeds were the redressing of 
various wrongs. They were thought to be mighty 
helpers of men, and divine honors were paid to them 
both in Sparta and at Rome. The Romans believed that 
they received assistance from them, while fighting the 



Queries. 



The Constellations for March and April. 81 

Latins at Lake Regillus. In Macaulay's "Lays of 
Ancient Rome" is the following reference to their 
appearance : 

" So like were they, no mortal 

Might one from other know ; 

White as snow their armor was ; 

Their steeds were white as snow." 

According to one version of the story Castor was 
mortal, while Pollux was immortal. When Castor was 
dying Pollux prayed to be permitted to die with him. 
Jupiter did not wish to grant this request, but rewarded 
their attachment by allowing them both to spend 
alternate days on Mount Olympus and in Pluto's realm. 

Which is the brighter, Castor or Pollux ? What is 
the color of Castor ? Is Capella whiter than Castor ? 
Perseus. 

This constellation should be hunted up early in the 
month, as soon as it is dark ; at that time it is low in 
the northwest. 

A little more than half way from Capella to y Androm- 
edae, 3 north of the line joining them, lies a, which is 
at one corner of a small quadrilateral, the other stars of 
which are y, t, and r. A line from Polaris through the 
center of this quadrilateral, when prolonged n° further, 
meets /9, which is commonly called Algol, the Demon The Demon 
Star. Its magnitude varies from the second to the fourth 
in less than three days. The rest of the constellation 
is best learned by a study of Fig. 25. The entire 
length of the figure from rj to C is 27 °. The head of 
Medusa, which Perseus carries in his hand, is formed of 
Algol and the stars near it. The constellation bears no 
special resemblance to a man, much less to a bear. 
It might be a fair model for a baboon. 

Near the middle point of a line from y to d Cassiopeiae 



Description. 



Star. 



82 



A Study of the Sky. 



A cluster. 



Mythology. 



is a fine double cluster, distinctly visible to the naked 
eye, as a bright spot in the Milky Way. It is pretty in 
an opera-glass and fine in a small telescope. Here 
hundreds of suns are bunched together. This cluster is, 
for small telescopes, the finest visible in the United 
States. 

Perseus belonged to Jupiter's numerous family of 

demigods. Polydectes, 






Ye 

I 



v 



I 



Queries. 



king of a little island, 
fell in love with Per- 
seus' s mother. The 
young man opposed 
5? the king's wishes in 
this matter, and was 
therefore sent to fetch 
the snaky head of the 
monster Medusa, who, 
with her sister Gor- 
gons, was equipped 
#/ 6 w ith tusk-like teeth, 
brazen claws, and 
golden wings. So 
frightful was the aspect 
of a Gorgon that any 

Fig. 25,-Perseus. Qne who \ 00 ^ e ^ on her 

was turned to stone. Equipped with winged sandals, a 
magic wallet, a helmet which made him invisible, 
a sickle, and a mirror in which he viewed the image of 
the monster, he accomplished his task. In his home- 
ward voyage through the air he rescued Andromeda, 
the Ethiopian maiden, and married her. 

Is Algol as bright as y ? Is Algol as bright as a. ? To 
what star in Perseus does a line joining the centers of 
the two clusters mentioned above point ? 



+ 



The Constellatiojis for March and April. 83 

Cancer. 

The principal stars of Cancer form an inverted Y (Fig. _ 

. . . . \ . Description. 

26), which is on the meridian at 9 p. m., in the middle 

of the month. The total length 

of the x is 20 , and all the stars 

in it are of the fourth magni- "l 

tude. A line from Polaris to J 

Ursae Majoris, when prolonged 1 

40 ° further, ends near the cen- 1 

ter of the \. Near the middle 

point of a line joining d and y 

lies the cluster of Praesepe, the / 

Bee-hive, which falls an easy 

prey to an opera-glass. To 

the naked eye it is a hazy spot. 

Two degrees west of a is an- / \ 






\ 



\ 



other cluster almost visible to / \ 

the naked eye ; a good opera- / 

glass brings it out. ^L. \ 

When Hercules was having • Q, N 

a desperate battle with the 



■f- 



nine-headed Lernean hydra, a 

gigantic crab came to the FlGl 26 -~ Cancer - J^ 

assistance of the hydra, and succeeded in wounding the 

hero. 

Canis Major. 

The chief jewel of this group is Sirius, brightest of the DeS cri P tion, 
fixed stars, which is readily found by prolonging the 
belt of Orion 20 eastward. The Dog sits upright, 
facing his master Orion (Fig. 28). Sirius burns in his 
head. The triangle formed by d, e, and yj is in his 
haunches. /? is at the extremity of his uplifted fore paw. 
He is evidently in the attitude of begging for a bite of 



84 



A Study of the Sky. 



Sirius. 



Discovery of 

companion. 



the hare under Orion's feet. His hind legs stretch for- 
ward to Z and X. A fair cluster, barely visible to the 
naked eye, is situated near a point one third of the way 
from Sirius to ?. A small telescope reveals a red star in 
the center, which is brighter than its companions. S 
and ~ appear double in an opera-glass. 

Sirius is interesting not only from its brightness, which 

is seven times as great as that of Capella, but also from 

the fact that it is a remarkable double. A faint com- 

* panion, fairly 

-#^---^^ Sirius 

y w— ■--- ^_ 



within the blaze 
of glory which 
surrounds the 



tL 



U 



■4 



Fig. 27— Caxis Major. 



telescopic image 
of the bright star, 
is swung around 
once in fifty-three 
years. The dis- 
tance of Sirius 
from us is fifty 
million million 
miles; light 
comes from it to 
us in eight years. 



The companion 
was discovered by Alvan G. Clark, the optician.* 
When using Sirius to test the 18*2 -inch glass now at 
Dearborn Observatory, Evanston, 111., he suddenly 
exclaimed, "Why, father, the star has a companion ! " 
The real size of this splendid orb may be inferred from 
the fact that it radiates forty times as much light as the 
sun. A more complete history of it will be given here- 
after. 



; Of Cambridgeport, Mass. 



The Constellations for March and April. 85 

Cam's Minor. 

There are but two bright stars in this asterism, a and Description. 
ft (Fig. 29). a is commonly called Procyon. Procyon 
is 27 east of Betelgeuse (« Ononis). These two stars 
and Sirius form an equilateral .^ 

triangle. /? is 4 northwest of ^ ™ p 

Procyon. / 

Procyon is interesting for s 

several reasons ; it is one of ,.' 

the nearer stars, being but 9 ^VtyO/p 
seventy million million miles & 

away. It is moving quite rap- FlG - 28.-Canis Minor. 
idly, for a fixed star, along the face of the skv, re- „ 

. . ° J ' Procyon. 

quiring only 1,500 years to traverse a distance equal to 
the apparent diameter of the moon. This journey is not 
performed in a straight, but in a wavy line ; hence it is 
supposed to be swung from side to side by the attraction 
of one or more companions, not yet discovered. 
Lepus. 
Lepus, the Hare, lies beneath the feet of Orion, a 

i± q martyr to his proclivities Description. 

for hunting. With a 

/; 1 good opera-glass one 

T^vAf may see y double (Fig. 

' \ ... 27). The most remark - 

\ a ^^■^- able object in the con- 

^-^* stellation is the crimson 

» , ^" v . star R, which can be 

~^* A'^ seen with an opera-glass. 

"w^'' ' ^*^«^ 1 £ A line from a through 

' ~y~ p-t when prolonged 3 , 

fig. 29.-LEPUS. strikes it. Like most 

red stars it is variable, ranging in magnitude from 6.5 

to 8.5 in a period of 14^ months. 



86 A Study of the Sky. 

Leo. 
Description. This is a striking constellation, composed of a sickle 

and a large right-angled triangle (Fig. 30). It is just 
east of Cancer. A line drawn from Polaris to p. Ursae 
Majoris, which lies in the forward hind foot of the Bear, 
prolonged 22 °, meets y, the brightest star in the blade 
of the sickle. A line from Polaris through the center of 
the bowl of the Great Dipper, when extended, passes 
through the large right triangle, which is east of the 
sickle. /?, at one vertex of the triangle, is often called 
Denebola ; a, at the end of the handle of the sickle, 

Fig. 30.— Leo. 

is Regulus. The distance from Regulus to Denebola is 
25 °. The lion is crouching ; the handle of the sickle is 
in his breast, and the blade in his head. The triangle is 
in his haunches ; his tail and hind legs are represented 
by a few scattered stars south of the triangle. 

The position of Regulus was determined by Babylo- 
nian astronomers 4,000 years ago. By its change in 
longitude* Hipparchus discovered the precession of the 
equinoxes 2,000 years ago. Regulus and Denebola 
Double stars. have each companions of the eighth magnitude, which 

* Longitude is like right ascension, except that it is measured along the 
ecliptic, instead of the equator. 



Regulus. 



Mythology. 



The Constellations for March a?id April. 87 

can be seen with a powerful field-glass. y consists of a 
couple of bright revolving suns, which form one of 
the finest of such pairs. C is a double, which a fair 
opera-glass can handle. 

This asterism is found in all the most ancient repre- 
sentations of the zodiac ; the classic writers, however, 
have connected it with the story of the labors of Her- 
cules. They state that it is the gigantic lion which rav- 
aged the Valley of Nemsea. Hercules having found 
that his club and arrows were of no avail against this 
prodigy, gripped him by the throat and strangled him. 
King Eurystheus was so frightened, when Hercules 
returned with the dead lion upon his shoulders, that 
he ordered the hero thereafter to narrate his exploits 
outside of the city walls. 

Is Regulus as bright as Procyon ? Of what color is y ? 
A line drawn form y to e, prolonged 5 , meets a star 
of what magnitude ? 

CONSTELLATIONS FOR APRIL. 
Bootes. 

The later in the evening one can observe Bootes, the 
better it will be seen. On April 1 at 9 p. m. it is low in Description, 
the northeast, its principal stars forming a kite-shaped 
figure 25 in length (Fig. 31). The side from a to d is 
lowermost, a is a star of the first magnitude, better 
known as Arcturus. A line from Polaris to a group of 
three fourth magnitude stars, which form a small triangle 
5 from the end of the handle of the Great Dipper, pro- 
longed an equal distance, strikes Arcturus. A line from 
Polaris to /? Ursae Minoris, the brightest star in the bowl 
of the Little Dipper, prolonged 35 ° meets ,3, which is at 
the summit of the kite. A line from Polaris to the star 
in the end of the handle of the Great Dipper, when pro- 



Queries. 



88 



A Study of the Sky 



A double star. 



Arcturus. 






ir f 



longed an equal distance, ends near Arcturus at a small 
triangle composed of a third, a fourth, and a fifth magni- 
tude star. These three stars form a tail for the kite. 
On the other side of Arcturus, at an equal distance, lies 
another small triangle, likewise composed of stars of the 

third, fourth, and 
fifth magnitudes. 
These two trian- 
gles mark the feet 
of the bear-driver. 
Arcturus is in his 
sword ; 3 and y are 
respectively in his 
right and left 
shoulders, while /3 
marks his head. 
The little triangle 
near the end of the 
handle of the 

jB ~3f ^eat Dipper is in 

CL < his uplifted left 

hand. 

£ is a fine double, 
as seen with a glass 
four inches or more 
a aperture ; the 
colors of the components are golden yellow and blue. 
Its beauty has won the appellation of "pulcherrima. " 
Over 1,200 years are occupied by one revolution. 

Arcturus is a star of amazing magnitude. So far is it 
away that it is impossible to measure its distance with 
any sort of accuracy. One of the latest measures makes 
its distance 1,000 million million miles. From this 
is derived an estimate that it is a million times as large 



flrdtirus 






Fig. 



-Bootes. 



Mythology. 



The Constellations for March and April. 89 

as the sun. Its diameter is then 100 times that of the 
sun. The reason for this is readily grasped by consider- 
ing two cubes, one of which has each edge a foot long, 
while each edge of the other is 100 feet in length. The 
second cube is 100 times as long, 100 times as broad, 
and 100 times as thick as the first. Therefore it is 
100 x 100 x 100 times as great in volume. Arcturus is 
approaching us at the rate of five miles a second, but 
this is only one component of its motion. It moves 
along the face of the sky at the rate of 300 miles a 
second, if the preceding assumption about its distance is 
correct. 

The mythological story usually accepted is that this 
constellation represents Areas, the son of Callisto. 
When his mother was changed into a bear (Ursa Major) 
Areas, not recognizing her, was about to slay her in the 
chase, when Jupiter prevented so unfortunate a deed by 
taking them both to the sky. The name Bootes is used 
by Homer, and signifies "a plowman." The Great 
Dipper has been often called a plow, though Homer 
calls it a wagon. It seems likely that Homer regarded 
Bootes as being either the driver of the wagon, or the 
guide of the plow. 

What is the color of Arcturus ? What is the color of 
e ? Does Arcturus rise north of the east point of the 
horizon, or south of it? 

Coma Berenices. 

Only two stars in this little group are as bright as the 
fourth magnitude. There are sixteen stars of the fifth 
magnitude, and about seventy-five fainter stars, which 
can be seen with the naked eye. All these lie between 
the large triangle in the haunches of Leo and the kite 
in Bootes. The constellation contains many small neb- 



Queries. 



9Q 



A Study of the Sky. 



ulae, but a large telescope is required -to show them well. 
The most crowded part of Coma is a pretty sight in an 
opera-glass. 
History. Berenice is an historic personage, the wife of Ptolemy 

III. When her husband went to war against the 
Syrians, she vowed to sacrifice her beautiful hair, in case 
he returned safely. The sacrifice was made, and the 
Alexandrine astronomer Conon commemorated it by 
establishing this constellation. 

Virgo. 
This constellation lies south of Coma Berenices and 

ft 






-tr 






:^ 4<*< 



Description. 



Spica. 



Fig. 32.— Virgo. 

Bootes, and east of Leo. The principal stars can be so 
connected as to form an outline of the flowing robe of a 
virgin (Fig. 32). She is in a recumbent posture, lying 
nearly along the equator, her head being just south of ft 
Leonis. «, a star of the first magnitude, has the proper 
name Spica, and forms an equilateral triangle with Arc- 
turus and ft Leonis. The right arm of the Virgin is 
extended to e, and the left hand reaches down to grasp 
a spike of wheat at Spica. The celestial equator runs 
through the stars X, and 7? on opposite sides of her body. 
Spica is very remarkable in that it consists of two re- 
volving bodies which occupy but four days in one revo- 



The Constellations for March and April. 



9i 



Nebulae. 



lution. It has never been seen double, but the periodic 
shirtings of the lines in its spectrum have shown its 
duplicity. 

y is .a fine double, composed of two equal suns. It is 
now resolvable without difficulty by a three-inch tele- 
scope. The period of revolution is 175 years, a little 
more than that of Neptune about the sun. 

Between Coma and the upper half of the Virgin's body 
is a remarkable region, which is thickly sown with nebulae. 

In the Golden Age, when the gods dwelt upon the Mythology, 
earth, Astraea was a divinity whom men especially rev- 
erenced for her pure life and kindly deeds. She was 
the last of the immortals to leave the earth at the close 
of the Golden Age. 

Does Spica rise south of the east point of the horizon, Queries. 
or north of it ? Does a line from Spica to Polaris pass 
through the handle of the Great Dipper ? How many 
degrees from d to y at the Virgin's girdle ? 

Corvus. 

Corvus, the Crow, is further south than Virgo, and Descriptior 
may be seen in the southeast at 8 \^, 
p. m., any evening in April. The *f ^"" ^ ^ A 
four brightest stars form an easily 
recognized quadrilateral (Fig. 33), 
the eastern side of which is 7 in 
length. A line from 1 Virginis 
through Spica, prolonged west- 
ward 1 5 , passes through the two 
stars in the northern side of the 
quadrilateral. «, the lowest star in 
the diagram, is in the beak of the 

Crow, which stands upon the body of Hydra (yet to 
be described), pecking at it. 



/S 



Fig. 



a 

-Corvus 



V 

\ 
\ 
\ 



9 2 



A Study of the Sky 



Mythology. 



Queries. 



Description. 



A temporary 
star. 



Mythology. 



Description. 



W 






Corvus was Coronis, a mortal princess, who was 
transformed into a crow by Minerva. 

What is the color of ft ? Which star is the brightest 
of the group ? How far from 8 is the nearest visible 
star? 

Corona Borealis. 

The Northern Crown is a very satisfactory group, be- 
cause the eye at once recognizes a similarity to the ob- 
ject which it is supposed to represent (Fig. 34). The 
1 constellation is just east 

of the middle of the 
kite in Bootes. At the 
end of April it does not 
£ cross the meridian till 1 
a. m. It is, at that time 
in the month, well up in 
the northeastern sky at 
9 p. m. a, also called 
Alphecca or Gemma, is 
io° east of e Bootis. 
Coronae, one of the small 
number of temporary stars. In May, 1866, it blazed 
forth suddenly, equalling Alphecca in magnitude. 
After it was discovered it declined in brightness, and 
had sunk below the eighth magnitude by the end of the 
month. An opera-glass now shows it as a star of the 
ninth magnitude. 

The crown belongs to Ariadne, whom Bacchus made 
his wife. He gave it to her at the time of the marriage, 
and afterward placed it among the stars. 

Hydra. 

Hydra is an immense snake, whose head is just south 
of the \ in Cancer ; the end of its tail is south of the 



>* 



% 



Fig. 34.— Corona Borealis. 

south of e is situated T 
temporary stars. 



The Constellations for March and April. 93 

feet of Virgo, a, also called Cor Hydrae, is in its heart 
(Fig. 35). A line from Polaris running in front of the 
sickle in Leo (being 4 away from e Leonis, which is at 
the point of the sickle-blade), when prolonged to a 
point 25 ° distant from a Leonis, meets Cor Hydrae. 
From Cor the snake's body winds eastward and south- 
ward, passing immediately beneath Corvus, and stretch- 
ing 30 eastward to a group of small stars, which lies 
20 south of fi Virginis. A line from d Corvi to e Corvi 
prolonged 13 meets c. 

Chinese astronomers are said to have particularly ob- 
served Cor Hydrae over 4,000 years ago. Their records 



/ 



Fig. 35. — Hydra. 

show that in the reign of the emperor Tao it crossed the 
meridian at sunset, at the time of the vernal equinox 
(March 20 in the modern calendar). 

e is a fine double for a three-inch telescope ; one 
component is yellow, the other blue. 

Hercules was sent to kill a monster which was ravaging 
the country of Lerna, near Argos, and which has been 
called the Lernean hydra. It had nine heads, one of 
which was immortal. Whenever Hercules struck off a 
mortal head with his club, two others grew out to take 



Cor Hydrae. 



Mythology 



Queries. 



94 A Study of the Sky 



its place. He finally burned the mortal heads, and 
buried the immortal one under a rock. As is fitting, 
we find the immortal head in the sky, close by Cancer, 
the Crab, which assisted Hydra in the fight and suc- 
ceeded in wounding Hercules. 

What is the color of Cor Hydrse ? A line from e 
Corvi to /5 Corvi, prolonged eastward io°, strikes what 
star in Hydra ? At the end of the tail of Hydra are two 
fifth magnitude stars 3° apart ; how many faint stars 
can be seen between them ? 



CHAPTER VI. 

THE CONSTELLATIONS FOR MAY AND JUNE. 

"Awake, my soul, 
And meditate the wonder ! Countless suns 
Blaze round thee, leading forth their countless worlds." 

— Ware. 

Lyra. 
One who looks for this constellation early in May 
should observe it as late in the evening- as is convenient. 
At 9 p. m. it is in the northeast, not very high up. It 
will probably be recognized at once because of the bril- 
liancy of Vega, its lead- , ^ 
ing star (Fig. 36). The -&- 
parallelogram formed by N ^^ VfyG 
ft, y, $, and C will be be- ^ S Q 
low and at the right of 
Vega. The distance from 
Vega to /? is only 8°. / 
Vega is nearly equidistant 



Description. 



! 

I 



i ; 

from Polaris and the star / 






at the end of the tail of 
the Great Bear, being 
over 40 from each. FlG - 36.-Lyra. 

Vega is one of the most beautiful, as well as one of 
the brightest stars. It is 120 millions of millions of 
miles from us, and thirty times as bright as the sun. 
Light consumes twenty years in coming to us from it. 
It is approaching us at the rate of ten miles a s-econd. 
It will be the pole-star 12,000 years hence. 

£ is one of the most famous of multiple stars. An 
95 



9 6 



A Study of the Sky 



Epsilon Lyrae. 



A variable. 



An elliptical 
nebula. 



Mythology. 



Queries. 



average eye perceives that it is oblong, and a good eye 
splits it into two. With a three- inch telescope each of 
the stars is again divided into two components. Both 
pairs revolve, one in a period of 2,000 years, the other 
in 1,000 years. 

/? is a variable star, which changes from magnitude 
3.3 to 4.5, being alternately brighter and fainter than y. 
Its period is nearly thirteen days. There are curious 
anomalies in its changes, for which astronomers have yet 
found no reasonable explanation. 

The only elliptical nebula which a small telescope will 
show is one third of the way from ft to y. In a large 
telescope it is an exceedingly beautiful object. Were 
the sun in the center of it, the planet Neptune would not 
lie outside of it. 

Lyra is the golden harp given by Apollo to Orpheus : 
not only wild beasts were charmed by its sweet strains, 
but even trees and rocks, which moved from their places 
to follow the harper. With it Orpheus descended to 
Hades, stopped the sound of torment by its music, and 
won back his dead wife, melting stern Pluto's heart. 

Is d double to the naked eye ? What is the color of 
Vega ? Is Vega above the horizon more or less than 
twelve consecutive hours ? 



Heracles. 



A large part of Hercules lies between Lyra and Co- 
Description, rona Borealis. It therefore appears to be above Lyra 
when seen low in the east. During May a better view 
of it can be obtained after 9 p. m. than before that hour. 
The giant is represented with his head toward the 
equator and his feet toward the north pole (Fig. 37). 
a is in the head ; the shoulders are marked by /5 and d ; 
e and X are in the belt. The positions of the limbs 



The Constellations for May and June. 97 

are indicated by dotted lines in the diagram. The 
entire length of the figure from a in the head to r in the 
right foot is 35 . a is nearly 30 from both a Lyrae 
and a Coronae. /3 is nearly half way from a to a 
Coronae. The extremity of the left arm is marked by 
a small group less than two thirds of the way from a to 
a Lyrae. 

a is a fine double star, which a two-inch telescope can a fine double. 
resolve ; the companion is blue. 

One third of the way from -q to C is the finest globular The great 
cluster in the northern £ cluster!*" 

hemisphere. It is vis- 
ible to the naked eye w fc ± s 
on a dark night. With 

a small telescope it \ "^7 

looks like a nebula. 
A large glass resolves 
it into thousands of 
small stars, which are 
crowded together into _4~-% , 

one glowing mass in ° 1< ~^----*<f ♦ 

the center, from which * , / y¥ 

streams radiate out- 
ward like the arms of ', 
a star-fish. When one » /' 
reflects that each star ~if' a 
is a sun, and that the FlG - 37-Herculbs. 
distance of the cluster from us is so amazing that astron- 
omers have not been able to measure it, or even to 
discover any changes in the relative positions of the stars 
due to their mutual attractions, the grandeur of the sys- 
tem fairly appals the imagination. 

The region of the heavens in which Hercules lies is of 

..." Our goal. 

special interest, because several astronomers have shown 



** ff 



** 



y« 



Queries. 



Description. 



98 A Study of the Sky. 

that the sun with his attendant planets is moving in that 
direction. 

Hercules is the giant whose marvelous strength was 
Mythology. celebrated so often in Greek legends. The most famous 
of his exploits were the twelve labors, which he per- 
formed at the bidding of Eurystheus. The constella- 
tions of Leo, Draco, Hydra, and Scorpio are all con- 
nected with the stories of these exploits, which may be 
found in detail in a classical dictionary. 

What is the color of a ? What is the appearance of 
the great globular cluster to the naked eye on a moon- 
less night ? Toward what star in Corona does the belt 
point ? 

Cygnus. 
Cygnus lies east of Lyra ; it is often called the 
Northern Cross, because the chief stars form an excellent 
Roman cross (Fig. 38). When seen low in the east the 

cross appears to 

^T " lie on its side ; 

the upright piece 

/ is over 20 long, 

___ ypj and extends from 

ft \ / «, also called 

^ Deneb, to ft, or 

/ /x Albireo. The 

^t't cross-piece runs 

,,'Wl \ from to e. The 

-#j ^' v v bill of the Swan is 

T^ at/?j and the out- 
fig. 38.— Cygnus. stretched wings 

are shown by the dotted line from fc to ft. y, at the in- 
tersection of the upright and cross-piece, is 18 east of a 
Lyrse, and a little nearer to Polaris. A line from /S 
Lyrse to y Lyrse, prolonged 8°, reaches ,3. The cross lies 



The Constellations for May and June-. 99 

in a portion of the Milky Way which is rich in fields 

fine for an opera-glass. Some of the finest regions are Fine fields - 

within a few degrees of a ; they appear to the unaided 

eye simply as bright portions of the Galaxy. There are 

also some dark rifts near by, which strikingly contrast 

with the glories all about them. 

/? is, for a small telescope, the finest colored double in A co i ored 
the sky. A magnifying power of ten diameters splits it double - 
with ease. With larger telescopes the contrasted colors 
are seen finely by throwing the stars out of focus. 

61 is a star of magnitude 5.5, which is noted as the 
first star whose distance was measured. It is over 500,- 
000 times as far away as the sun ; only two stars are 
known to be nearer. 61 is 6° from e, and forms a par- 
allelogram with «, y, and e. 

A little less than one third of the way from « to k, one 
degree north of the fourth magnitude star o *, is 2 , 
which an opera-glass shows as a triple lying in a pretty 
field of smaller stars. 

The Latin poet Ovid states that Cygnus was a friend M tholo 
of Phaeton, the unhappy youth with whom the horses of 
the sun ran away. The friend's grief was so poignant 
that Jupiter changed him to a swan. . 

A line from a to a Lyrae, prolonged an equal distance, 
meets what star in Hercules ? A line from ft to a Lyrae, 
prolonged 13 , meets what star in Hercules? A line 
from y to a Lyrae points to what bright star in Hercules ? 



Queries. 



Draco. 

The head of the Dragon is marked by a conspicuous 
quadrilateral formed of /?, y, £, and v (Fig. 39). It lies 
just north of 1 Herculis, which is the giant's left foot. 
The distance from y to c is 5 . y forms an equilateral tri- 
angle with Polaris and the star at the end of the handle 



Description. 



IOO 



A Study of the Sky. 



Mythology. 



of the Great Dipper. The convolutions of the Dragon's 
form can be best learned from the diagram, with the help 
of the following data. The first fourth of the body lies 



between Lyra and the pole, 
and turns sharply, is nearly 

■♦■ 7h/ar/s 



Ys 



V7 






*y 






y 

-y- 3 



Description. 



s, where the body is coiled 
half way from Polaris to d 
Cygni. i may be 
found by prolonging 
a line from Polaris 
to y Ursae Minoris 
1 3°. A, at the end 
of the Dragon's tail, 
lies between Polaris 
and the bowl of the 
Great Dipper, and 
is 8° from a Ursse 
Majoris. «, which 
is about half way 
between C Ursae 
Majoris (Mizar) 
and y Ursae Minoris, 
was the pole-star 5,000 years ago. Its brightness has 
probably diminished much during the past two centuries. 
It was previously rated as of the second magnitude. 

There are two mythological stories with which this 
constellation is associated. The Thracian hero Cadmus 
slew a dragon which guarded a well from which he 
wished water. Minerva advised him to sow the dragon's 
teeth ; armed men sprang up from them. Another 
dragon, Ladon by name, who guarded the golden 
apples of the Hesperides, was slain by Hercules and 
placed among the stars. 

Sagitta. 
Sagitta, the Arrow (Fig. 40), is a neat little figure, 
which lies south of Cygnus. a and /5 mark the butt of 



Fig. 39. — Draco. 



The Constellations for May and June. i o i 

the arrow, and y is at its point ; the length of the arrow 
is 7 . A line from a Lyras to /5 Cygni, prolonged n°, 
meets y, and is nearly perpendicular to the arrow. The 
constellation, though small, offers a fine field for a small 
telescope. 

Two degrees southwest of the butt of the arrow lies e, posing 
of the sixth magnitude, which is a pretty pair in a good ob J ects - 
opera-glass. Less than 2° beyond the point of the 
arrow a small telescope _X_ 
will pick up a pretty triple y" * "* — -* ^ xjf 
star, 0. Four degrees r**"~~-»^5* 

from the butt of the X* 

arrow, toward the belt of 7^ 

Hercules, lies a cluster fig. 4o.-sagitta. 

visible with an opera-glass. A yellowish star of the 
sixth, magnitude, 2^° south of y, is the brightest of a 
group which shows nicely in an opera-glass, and con- 
tains a red star. 

Scorpio. 

In the latter part of May Scorpio is on the meridian 
in the south at midnight. The later in the evening one 
looks for it the better, for though many of the stars are 
very bright, the constellation being the most brilliant in 
the zodiac, they never get high in the heavens. The 
brightest star, a, is Antares (Fig. 41), and maybe found 
by prolonging a line from Polaris to /? Herculis, the pro- 
longation being two thirds as long as the original line. 
The curve, composed of /9, d, and -, is 7 in length, and 
resembles the blade of a scythe, the snath of which 
extends down to e ; Antares is at one of the handles. 
Below £ the curve is U-shaped, and ends at the bright 
pair X and u, which lie in the Milky Way and mark the 
animal's sting. The sting is 17 southeast of Antares. 
The distance from Antares to /? is 9 . 



Description. 



102 



A Study of the Sky. 



Antares. 



A rich cluster. 



Mythology. 



Antares is a magnificent double, having a greenish 
companion fairly within the blazing aureole about the 
principal star. This was discovered in a curious way. 
Ordinarily a small telescope will not show the com- 
panion, because of the overpowering brilliancy of the 
large star. But on one occasion in 1819, when the star 
was emerging from behind the moon, the small star 

f**"¥* popped out first, and 
Y was seen for an in- 
w \ stant before the large 

w one appeared. 

/S is a fine double 
for a two-inch tele- 
scope, v is 2 east of 
ft, and is much easier 
to split than /?. A 
large telescope di- 
vides each compo- 
nent of v again, mak- 
ing ita quadruple star. 
Half way between Antares and /? lies a cluster, which 
Herschel described as the richest and most condensed 
mass of stars in the firmament. It is visible with a small 
telescope, but a large one is needed to bring out its 
beauty. In May, 1862, a star blazed out, apparently 
in the center of the cluster, almost extinguishing the 
latter by its brightness ; in less than a month it faded 
into invisibility. 

One of the mythological stories connects a scorpion 
with the story of Orion, stating that the mighty hunter 
boasted that he would kill all the wild beasts on the 
earth, whereupon the earth sent forth a scorpion which 
stung and killed him. When ^sculapius attempted to 
bring him back to life, Jupiter, knowing that Orion had 






-*-£ 



h 



Fig. 41.— Scorpio. 



The Constellations for May and June. 103 

already experienced his full share of life's sorrows, 
smote the physician with a thunderbolt. 

What is the color of Antares ? Which is the brighter, Q Uer ies. 
{i or d? At about what point of the horizon does 
Antares set ? Is Antares above the horizon twelve con- 
secutive hours, or fewer ? 

THE CONSTELLATIONS FOR JUNE. 

Libra. 

The principal stars of this constellation form a rude Description, 
square (Fig. 42), which lies half way between the feet of 
Virgo and the scythe-blade in Scorpio. The distance 
from a to /? is 9 . a, which lies on a line from fi 
Scorpii to a Virginis, 1 /*• 

appears elongated to a /I 

keen eye ; it falls an y y 

easy prey to an opera- ^' 

glass. Near the middle f 

point of a line joining [i qfT fi 

to }j. Virginis is 8. a star / \ 

of the fifth magnitude, / / n 

which is a very remark- / / N 

able variable. In five ^ // v 

and a half hours it sinks t\ ' \ 

to the sixth magnitude ; S N ^&" O 

six and a half hours \ , y ' 

afterward it has regained N \ ,' 

its former brightness, liL^ 

and remains in that es- T£ 

tate for forty-four hours, FlG - 42.— Libra. 

after which it fades again. Its entire period is fifty-six 
hours. 

Libra was originally a part of Scorpio, forming the History. 
claws of that venomous animal. The Egyptians are 



104 



A Study of the Sky. 



Queries. 



Description. 



A fish story 



said to have formed it into a separate constellation as 
early as 300 B. C. In the time of Augustus Caesar it 
was regarded as the balance belonging to Virgo, the 
goddess of justice. 

What is the color of ft ? Where are sixth magnitude 
stars more thickly sown, northeast or southeast of the 
' ' square " ? A line from y to Polaris passes through 
what small but plain constellation ? 

Delphinus. 
A line from Polaris through o. Cygni, prolonged 30 , 
ends at a small diamond-shaped figure (Fig. 43), which 
contains three stars of the fourth magnitude and one of 
the third. The length of the dia- 
mond from ft to y is 2^°. In- 
cluding e we have a wedge-shaped 
figure which has been called 
"Job's Coffin." 

y has a bluish companion of the 
sixth magnitude, which a two-inch 
telescope will show. 

The dolphin is supposed to be 
the fish upon whose back Arion, 
the ancient bard and musician, 
took his celebrated ride. When 
he was returning to Corinth from Sicily, where he had 
won a prize in a musical contest, the treasures which 
had been presented to him roused the cupidity of the 
sailors, who planned his murder. Obtaining their per- 
mission to play the cithara once more, he charmed a 
school of dolphins by his melodies ; he then leaped into 
the sea, and was brought safely to land by one of them. 

Aquila. 
This constellation lies just south of Sagitta, and rises 









Fig. 43. — Delphinus. 



The Constellations for May and June. 105 

near the east point of the horizon ; in the middle of June 
it is on the meridian at 2 a. m. It will therefore be Description, 
best not to look for it before 9 p. m. Altair, its prin- 
cipal star, may be located by a line from Polaris through 
d Cygni ; it is flanked ^ V 

by the stars /? and y ' v x 

(Fig. 44), which >"»''•« \ 
form with it a line X-g x 

5 long, running / \ 

athwart the Galaxy. ' <$[ 

This line prolonged / ' \ 

southward8° strikes j ^z. ^ \ 

0. The rest of the V - ' " --^ ^ \ 

figure, which bears ' " ~> -^ ^\* 

not the remotest re- ^ :^- 

semblance to an • 

eagle, is easily found IG ' 44 '~ QUILA - 

by the help of the diagram. Altair is a million times as 
far from us as the sun, its light taking sixteen years to 
reach us. >j, which is 8° south of Altair, is a well-known 
variable, having a period of seven days and a fraction, in 
which it loses and regains over a magnitude. Its vari- 
ations can be well seen by comparing it for a few nights 
with and c, which are near by. 

Aquila is, according to one account, the eagle of Ju- 
piter, which stood by his throne. Another story is that 
Merops, a king of the island of Cos, attempted suicide, 
wishing to follow his wife to the under world. Juno's 
proverbial kindness of heart led her to thwart this wish, 
by placing him among the stars, in the form of an eagle. 

The line of three stars, in which Altair lies, when pro- 
longed northward, passes through what brilliant star? 
What is the color of Altair? Does a line from I to 
Polaris pass through a Lyrse ? 



Mythology 



io6 



A Study of the Sky. 



Description. 



Serpens and Ophiuchus. 
We treat these constellations together, since they form 
the one figure of a man grasping a serpent (Fig. 45). 
Ophiuchus, the serpent-bearer, is between Hercules and 
Scorpio. The head of the serpent is marked by the 
triangle formed of '', y, and a\ in the upper right hand 
corner of the diagram ; it lies io° south of Corona. 



y-*K* 



-V, 



A „--'" 



♦ 



</•-' 

** 



* ri 



The serpent 
turns. 



Fig. 45.— Serpens axd Ophiuchus. 

Thence the body of the serpent runs southward through 
a and e Serpentis to d and e Ophiuchi, where one 
hand of Ophiuchus grasps the snake. The next two 
stars in it are ~ and 33 Ophiuchi. The distance from 
a Serpentis to £ Ophiuchi is 22 °. These two stars form 
with / Ophiuchi and :->- Serpentis a fine parallelogram. 
From r t Ophiuchi the snake's body goes eastward 
and northward, as shown in the diagram, ending at 
Serpentis, which is on a line from Polaris to y Lyrse, 



The Constellations for May and June. 107 

prolonged 30 further ; is also 7 west of d Aquilae. 

a Ophiuchi, which marks the man's head, can be 
found by drawing a line from Polaris to /? Draconis, and 
prolonging it an equal distance. It may also be located 
by a line from a Bootis to the head of the serpent, pro- 
longed as far again, a Herculis is but 6° from a 
Ophiuchi. (3 and y are in the right shoulder of Ophiu- 
chus, 1 and fc in his left. His right knee is at rj, and his 
left at C ; his right foot is at 0, and his left stands on 
Scorpio, close to a Scorpii. While Serpens is compara- 
tively easy to learn, Ophiuchus requires some attention ; 
therefore we have entered into considerable detail. 

One third of the way from Serpentis to a Ophiuchi 
an opera-glass will pick up a cluster. In the same line, clusters 
not far from a, is another cluster almost bright enough 
to be visible to the naked eye. There are many fine 
double stars and clusters in these constellations, but they 
are chiefly for good-sized telescopes. 

Ophiuchus is supposed to represent ^Esculapius, the 
god of medicine. Many temples were erected in his 
honor in various parts of Greece, and were used as hos- 
pitals, as well as for worship. Tame serpents were kept 
at Epidaurus, the principal seat of his worship, and the 
god himself frequently assumed the form of a serpent. 

Which is the nearer to a Herculis, the head or the 
left shoulder of Ophiuchus ? A small triangle of stars is Queries 
5 southeast of J3 Ophiuchi ; what are their magnitudes ? 
Two fifths of the way from a Ophiuchi to 0, the last star 
in the serpent's tail, is a double star 72 Ophiuchi ; what 
is its magnitude ? 

Sagittarius. 

This constellation is next to Scorpio, and east of it. 
In the middle of June it is on the meridian at 1 p. m. 
It is best therefore not to study it till 10 p. m., or else 



Mythology. 



Description. 



The "milk- 
dipper." 



Description. 



108 A Study of the Sky. 

to wait till the latter part of July, when it can be seen 
well at 9 p. m. The eye at once perceives the "milk- 
dipper" (Fig-. 46), the bowl of which is upside down, 
and is defined by the stars C, r } <r, and c ; / is in the end 
of the handle, and is io° from r. Sagittarius is a 

_x u Centaur, who is 

shooting at the 
Scorpion. The 



/ 

/ 
/ 



y bowl of the milk- 



CT ^^ dipper is in his 

^^^-"^X \ body. /, 0, and 

^f- y ' <P^^ \ £ represent the 

\ '' "^^- bow on which 



+' 



V ' T y there is an arrow, 

' whose tip is at y. 

I £ In the latter 

part of August, 
N ^ fj . when the constel- 

lation is on the 

Fig. 46. — Sagittarius. ■ i- r 11 • 

4 meridian, full in 

the south at 9 p. m., one may well explore the Milky 
Fine fields. Way in and above Sagittarius, with the help of an 
opera-glass or small telescope. There are several fine 
clusters and beautiful fields. Their whereabouts are in- 
dicated to the naked eye by bright spots in the Galaxy. 

Cepheus. 

Cepheus lies between Cassiopeia and Draco. The 
five brightest stars form a rude square surmounted by an 
isosceles triangle (Fig. 47). The entire figure is 20 
long, y is I2 ° from Polaris, nearly on a line from it to /9 
Cassiopeiae. a forms an equilateral triangle with Polaris 
and e Cassiopeiae. A line from y to «, prolonged an 
equal distance, meets a Cygni. King Cepheus sits behind 



The Constellations for May and June. 



109 



his wife Cassiopeia ; his head is marked by C and two 
fainter stars close by it ; his foot-stool is the tail of 
the Little Bear ; y is in his left s ^ 
knee ; the rest of his figure may y WT 

I \ 



\ 



^ 



A variable 
double. 



ey 



/ 



Fig. 47.— Cepheus. 

magnitude varies 



be supplied as one pleases. 8 
is a variable which has a period \ 

of 5^3 days, and ranges in magni- 
tude from 3.7 to 4.9. A good 
spy-glass reveals its duplicity ; the 
two stars are respectively orange \ 
and blue. /5 is also a double, the '• 
large star being white, the small 
one blue ; a two-inch telescope 
handles it nicely, p, perhaps the 
reddest naked-eye star visible in 
the United States, is located 4 
from C, toward a, but south of a 
direct line between the two. Its 
irregularly from 3.7 to 4.8. 

Cepheus, like some men nowadays, was best known 
through his family. The "Classical Dictionary" says 
sententiously of him, " King of Ethiopia, son of Belus, 
husband of Cassiopeia, and father of Andromeda, was 
placed among the stars after his death." 
Capricornus. 

This constellation is east of Sagittarius. The line of 
a Aquilae (Altair) and its two immediate comrades, ex- Descr i pt i on 
tended southward, strikes into the heart of it. We shall 
not try to imagine that it is a goat, but rather the cross- 
section of a row boat (Fig. 48). The distance across 
the boat from a to 8 is 22 °. A line from Polaris to y 
Cygni, prolonged an equal distance, ends at «, which 
the naked eye shows as a double. An opera-glass 
shows /? to be double. By noticing that there is a pair 



Mythology. 



no A Study of the Sky. 

Pairs of stars. °f stars at each corner of the figure, one will have no 
difficulty in picking out the outline of the constellation 
in the heavens. 

A good view of Capricornus cannot be obtained dur- 
ing June until after midnight. In the latter part of 

a 



N 


1 U ^ 

1 




V.; 




'-*» 




Fig. 48. — Capricornus. 



August it reaches the meridian before n o'clock, and 
is well situated for observation at 9 o'clock. 

The mythology of this constellation is ' ' confusion 

Mythology. worse confounded. ' ' One who tries to study it up may 

be pardoned for wishing that Jupiter had given the goat 

a nice pasture in his back yard, and kept it out of sight 

of mortals. 



CHAPTER VII. 

THE ASTRONOMER. 

" Priest-ministrant within this mighty Fane, 
Whereon thou standest now is holy ground ; 
Divinest gift is thine — to gaze the first 
On glories yet unseen by mortal eyes." 

—A. V. G. 

Students of English literature in our colleges are . 

& ° An author and 

now encouraged, when studying the works of any his works. 
particular author, to study the man as well, to become 
familiar with his daily life, to learn his personal history, 
to study his habits and his environment. In this way 
one is the better equipped to understand and to criticise 
his works, for the man is pretty sure to be reflected in 
his writings. Learning his point of view, we can the 
better appreciate the conclusions which he reaches, and 
can make allowance for his personal bias. If he be a 
thoroughly lovable man and an inspiring writer, we gain 
a greater uplift from unconsciously associating the man's 
character with his productions. 

If this method is valuable in English literature, why 
should it not be in astronomy? Almost all of our anaiyze 

i 1 ■, c p . i • • r astronomers ? 

knowledge oi astronomy comes irom the writings of 
men who state that they have perceived this and that, 
that they have made such and such measurements, that 
they have drawn certain conclusions. Why should we 
not inquire into the characters of these men ? If some 
astronomer, who is noted for his powerful fancy, 
announces that he has found strong evidence that 



112 



A Study of the Sky 



Specialists. 



An astronomer 
denned. 



Jupiter has intelligent inhabitants, why should we not 
discount his statements because of the exuberance of 
his imagination ? An astronomer, whose work is the 
observation of comets and asteroids, together with com- 
putation of their orbits, expresses an opinion on a 
recondite point in solar physics. Certainly his opinion 
should not have much weight in comparison with that of 
a special student of the sun. It may be that astron- 
omers in general are altogether too conservative, and 
unwilling to welcome a piece of work which appears to 

overthrow some re- 
ceived theory. 

No further illus- 
trations are needed 
to show that the 
personality of the 
observer is a pow- 
erful factor in his 
scientific utterances. 
Let us therefore sub- 
ject the average as- 
tronomer to a pretty 
thorough analysis, 
so that we may un- 
derstand him and 
his work the better. 
Who, then, is the 
astronomer ? Is he 
the long-haired man 
who stands upon the 
street corner and 
sells a peep through his telescope for ten cents ? By no 
means. Is he the wealthy gentleman who is deeply in- 
terested in the science, and has a private observatory, 




Fig. 49.— Charles A. Young, Professor of 
Astronomy at Princeton University. 



The Astronomer. 113 



An original 
investigator. 



His physique. 



in which he spends quite a little time surveying the 
wonders of the sky ? Not at all. Is he the professor 
who has charge of an observatory, and uses its instru- 
ments for the instruction of the college students ? Not 
usually. 

The astronomer, whether in charge of an elaborate 
observatory, filled with costly instruments, or simply 
the possessor of a good opera-glass, or small portable 
telescope, is the man who by patient study of the sky 
adds to the sum total of astronomical knowledge. It is 
possible to be an astronomer if possessed of no optical 
instruments except a pair of good eyes, but the range of 
naked-eye work is extremely limited. The original 
investigator, then, is the man to whom we shall pay 
attention. 

First as to his physique. He may be tall or short, 
broad shouldered or slim, thin or tolerably fleshy, but 
he is almost always possessed of a good constitution, 
which will endure rigors of cold or extremes of heat, and 
will not break down under a severe pressure of work, 
night and day, year in and year out. 

His nervous system is well developed, his eyesight His nervous 
and hearing are fair, and his sense of touch is delicate. 
His hand is steady under trying circumstances. Ner- 
vousness is not a bane of his life, causing him to lose 
control of himself at moments when every faculty must 
be at its best, and every muscle obedient to his behest. 

When observing a transit of Venus, a repetition of 
which will not occur during his lifetime, he is, at the 
critical instants, as cool and collected as if sitting in his 
office, looking over a new book. This self-control 
comes from long training ; it finds a parallel in the 
steadiness with which a surgeon's hand, though pre- 
viously trembling, executes the crucial part of a difficult 



system. 



Self-control. 



H4 



A Study of the Sky 



Xi^ht work. 



Education. 



operation, when the life of the patient hangs in the bal- 
ance. This ability to exercise self-control is enhanced 
by the astronomer's plain living and regular habits. 

It is a mistake to suppose that he is ordinarily at work 
at all hours of the night, and tucks in bits of sleep partly 

by day and partly 
by night, under the 
direction of an alarm 
clock. For the 
majority of nights 
i are cloudy, so that 
no observing is 
done ; when the 
weather is clear 
he usually has on 
hand some work 
which comes during 
a certain portion of 
the night. He rarely 
works all night. 
Comet hunters are 
exceptions in the 




Fig. 50. 



-Edward S. Holdex, Director of 
the Lick Observatory. 



matter of regular- 
ity. They change their times of observing from night 
to night, working generally during those hours when the 
moon is below the horizon ; the faint objects which they 
discover are not commonly readily visible in moonlight. 
Astronomers are, on the whole, well-educated men, 
especially those who are the directors of large observa- 
tories. Very little can be done in their science without 
a sound knowledge of elementary mathematics. The 
principles of physics and mechanics come up continually. 
An American astronomer who cannot read scientific 
German and French with considerable ease is often 



The Astronomer. 



"5 



seriously hampered in his work ; for he must master the 
contents of many publications in those languages. Often 
he wishes to read Italian ; a knowledge of Latin and 
Greek is not infrequently of service. 

An astronomer may be very narrow-minded. The 
ceaseless round of computation by day and observation 
by night, demanding every iota of his time, has a strong- 
tendency to keep his mind from expanding along any 
other lines. But if, 
as usual, he has 
been through an 
old-fashioned, now 
much berated, col- 
lege curriculum, the 
liberalizing effect of 
the four years of 
study of various 
branches of knowl- 
edge keeps him 
from undue narrow- 
ness. It is note- 
worthy that men of 
only moderate men- 
tal caliber are the 
most likely to 
.shrivel up. The 
mental giants have 
a many-sidedness, 
which leads them to explore other realms of knowledge 
to a moderate extent. One of the best text-books on 
political economy published in this country is the work 
of an astronomer, most of whose time is occupied with 
directing intricate calculations belonging to the strictly 
mathematical side of the science. 




Fig. 51. — Simon Newcomb, Superintendent 
of the "Nautical Almanac" Office. 



Narrowness. 



Breadth of 
view. 



n6 



A Study of the Sky. 



Not a recluse. 



The value of 
time. 



Second after 
second. 



The director of a large observatory is continually 
brought into contact with men who are prominent in 
other lines of scientific work, and with those who have 
won success in various non-scientific walks of life. He 
also looks after the business interests of the observatory, 
and sometimes raises funds for the enlargement of its 
work. These circumstances effectually prevent his 
becoming a recluse. 

Astronomers have an inordinate sense of the value of 
time. A business man considers his own time very 
precious during business hours, and has no welcome 
for any one who consumes it needlessly. But after 

business hours are 
over he is at leisure, 
and whiles away 
much of his time in 
pleasurable occu- 
pations and social 
duties. All of an 
astronomer's wak- 
ing hours, except 
when he is at meals, 
are business hours. 
So great is the vol- 
ume of work which 
he would like to do, 
and so time-con- 
suming are the 
laborious computa- 
tions consequent upon his observations, that he is con- 
tinually urged to work at his topmost speed. Every 
minute counts. The very clocks, chopping off second 
after second, within his hearing, remind him that time 
flies, and that his mind must follow suit. By constant 




Fig. 52. — Benjamin A. Gould, Editor of the 
"Astronomical Journal." 



The Astronomer. 



117 




practice in estimating small fractions of a second he 
gains a mental alertness which is carried into all his Alertness. 
work. If he is explaining something, he expects the 
listener to grasp what he says instantly, and is well 
pleased if by any chance the hearer anticipates his ex- 
planation, and ar- 
rives quickly at the JP" ' "^& 
desired goal. 

The following in- 
cident will show how 
this mental quicken- 
ing came to a col- 
lege boy. He was 
a member of the 
junior class, and be- 
gan a. special course 
in practical astron- 
omy by learning to 
take time obser- 
vations. This work 
consists in observ- 
ing the times that some clock or chronometer reads, 
when certain known stars, in passing through the field 
of view of a particular telescope, appear to cross a num- 
ber of spider-webs placed at the focus of the glass. The 
construction of the instrument will be explained later. 

When a star's image crosses each spider-web, the 
observer is expected to note the reading of his time- 
piece. When observing by the " eye-and-ear " method 
he listens to the ticks of the clock, and tries to write 
clown, to the nearest tenth of a second, the time 
indicated by the clock when the star crosses each web. 
Quickness of perception and rapidity of thinking are re- 
quired for this. After the observations have been made, 



Fig. 53.— Edward C. Pickering, Director of 
the Harvard College Observatory. 



Sharp work. 



n8 A Study of the Sky. 

certain easy computations enable him to find the error of 
the clock ; then he compares this clock with the other 
timepieces of the observatory, to determine their errors. 

What was the effect of this work on the college boy ? 
He had been an easy-going young man, who was 
a lazy youth. content with learning his lessons fairly, and spending 
the remainder of his time in recreation. When on the 
street he had been in the habit of sauntering along as 
became a gentleman of leisure. When set to do some 
bit of manual labor he had been apt to distinguish him- 
self by the length of time which he consumed in the 
task. He played with his studies, as does a cat with a 
mouse, taking all the time he wished, and being satisfied 
if he was near the head of the class. 

But now a change came over him. He set for him- 
self a limited period of time in which each lesson must 
a change. ^ Q jnag^gj-g^^ \{ possible ; he placed his Greek or Latin 

text-book and his lexicon on the study-desk in such 
positions that their leaves could be turned quickly. He 
ceased his careless sauntering, and began to walk more 
rapidly. He filled otherwise unoccupied chinks in the 
day by reading selections from the best authors. He 
began to speak with greater rapidity ; when reading 
aloud, it was a mental strain for any one to follow him, 
for though the words were pronounced clearly, they 
were delivered like bullets from a machine gun ; he 
could read 475 words a minute. He seemed to have 
become thoroughly imbued with a conviction that no 
moments should be wasted, and that as much work as 
possible must be crowded into each minute of the day. 

If this was the effect of a few months of astronomical 
training on a college boy, what wonder is it that 
astronomers, after years of such work, gain special 
mental quickness ? 



The Astronomer 



119 



Another characteristic without which no man can 
become an accomplished astronomer is perseverance. 
At times he plunges for weeks and months through 
mazes of figures, the sight of which fairly wearies the 
beholder. Then again he devotes himself to the study 
of some abstruse problem with such furiousness of appli- 
cation that he seems able for the time to think of 
scarcely anything 
else. Fits of pro- Hg 
longed abstraction 
seize him, and cu- 
rious are the stories 
told of his actions 
when lost in con- 
templation. 

It is related of Sir 
Isaac Newton that 
he was once at- 
tracted by a fair 
lady, and paid court 
to her; in the course 
of an evening's visit 
he fell to musing. 
Reaching out his 
hand he took the 
young lady's and 
raised it gently 
toward his lips ; he 
carefully picked out the little finger on which to bestow 
the evidence of his affection. About this time the lady 
also became lost in pleasant thoughts. Sir Isaac 
squeezed her finger a bit, and stirred the hot ashes of 
his pipe with it. The rest of the story is short ; he re- 
mained a bachelor. 



Perseverance. 




Fig. 54.— William H. Pickering, of the 
Harvard College Observatory. 



Newton's 
courtship. 



120 



A Study of the Sky. 



Accuracy. 



Love of truth. 



Along with persistence goes a habit of unerring 
accuracy. The secret of this is chiefly that the whole of 
an astronomer's work tends to make him concentrate 
his attention on whatever is in hand. His whole mind 
is usually occupied with the particular work at which he 

. ._ ; has set himself. If 

. he is in the midst of 
the computation of 
a preliminary orbit 
of a comet, a single 
incorrect figure may 
vitiate all the suc- 
ceeding work and 
render his final re- 
sults worthless. So 
well lubricated is his 
mental machinery 
that he goes 
through intricate 
calculations without 
becoming confused, 
or falling a prey to 

Fig. 55.-Edward E. Barnard, of the a haunting fear that 

Yerkes Observatory. SQme blunder has 

been committed. As there are certain methods of 
testing the answers of examples in arithmetic, so there 
are occasional check-formulae, which the computer may 
use to test his work from time to time. The application 
of one of these formulae rarely convicts him of error. 

A habit of accuracy leads to love of accuracy, and 
love of accuracy leads to love of truth and hatred of 
error. One cannot converse long with an astronomer 
without noticing his love of accuracy and his evident 
endeavor to tell the exact truth. He despises untruth, 




The Astronomer. 



121 



and is a foe to prejudice of all kinds. If he hears a man 
putting forth argument after argument to bolster up 
some position, his mind naturally begins to search for 
facts which are opposed to the speaker's views. He has 
an inward contempt for any man who, instead of search- 
ing for truth, occupies himself with elaborating and 
defending some preconceived notion. He applies all 
reasonable tests to his own work, and attacks every 
important problem in as many ways as feasible, that he 
may obtain a series of independent results, from which 
the truth may best be wrought out. When he is engaged 
in original investi- 
gation, intellectual 
honesty is his king. 
Let us take a con- 
crete illustration of | 
this. 

A student who has 
not gotten used to 
astronomical ways is 

measuring a certain ' ^Mm^* 

angle. Each day he 
takes a set of ob- 
servations. His first 
three sets yield the 
following values : 

4 i° 51' 27". 1 

4i 5i 27 .9 

41 51 27 .0 
He measures the FlG - 
angle again and ob- 




56. — James E. Keeler, Director of the 
Allegheny Observatory. 



tarns 41 51' 25". 5. As this does not agree well with 
the previous results he feels disposed to reject it, and to 
tell no one about it, because it apparently proclaims him 



All sides of a 
question. 



A young man's 
quandary. 



122 



A Study of the Sky 



Rejection of 
observations. 



Freedom from 
bias. 



Independence. 



to be a poor observer. After thinking the matter over 
he asks the director of the observatory what he shall do 
with the discordant measure. The director inquires 
whether the observations seemed to be satisfactory at 
the time when he was making them, before he knew the 
result. The young man replies that while observing he 
thought he was doing accurate work, and that he does 
not believe that the instrument got out of adjustment 
during the observations. The astronomer informs him 
that if he has no reason for rejecting the last result, ex- 
cept that it does not agree with the former results as 
well as he would like to have it, he has no right to 
cast it out. Better to suffer the imputation of being an 
inaccurate observer than to sacrifice any honest work. 
The agreement of two or three observations does not 
prove that they are nearer the truth than some other 
observation, which disagrees with them. 

If any astronomer were known to be in the habit of 
giving a fictitious appearance of accuracy to his work 
by suppressing those observations which exhibited 
noticeable deviations from the others, all his work would 
at once be discredited by his scientific brethren, who 
would accuse him of ' ' cooking ' ' his observations. 
When one wishes to arrive at the truth he must take 
into consideration all the evidence, and not reject some 
of it, simply because it does not please him. 

If scientific men did nothing for their fellows except 
to impress upon them the necessity of bringing un- 
biased minds to the consideration of all important 
questions, and of being intellectually honest in their 
treatment of them, seeking the truth alone, their work 
would not be in vain. 

There is one more point in this matter of truth 
seeking, to which an astronomer pays special attention. 



The Astronomer. 



12 




Fig. 57. — First Position of the 
Spider-webs. 



He strives to make measures of the same quantity 
independent of each other. Suppose, for example, that 
he is measuring a double 
star. He sees the two 
stars, and two parallel 
spider-webs. The spider- 
webs are fastened in a 
brass box, which can be 
turned. He wishes to 
make the spider-webs 
parallel to a line joining 
the stars. He sets the 
spider-webs as in Fig. 57, 
so that it is plain that they 
are not in the desired 
position. He then turns the brass box in a left- 
handed direction, until the desired parallelism has 
been attained, as in Fig. 58. A certain silver circle, 
which is carefully divided into degrees and fractions of a 

degree, the readings of 
which change as the box 
holding the spider-webs is 
turned, is next read. In 
Fig. 59 is given a view of 
the rotating box and the 
graduated silver circle. 

The box is then moved 
again till the spider-webs 
stand in the position 
shown in Fig. 60. From 
that position the astrono- 
mer brings them back to 
parallelism with an imaginary line joining the stars, as 
before, and reads the circle again. By observing thus in 




Fig. 



58.— Second Position of the 
Spider-webs. 



A double star. 



Another 
measure. 



I2 4 



A Study of the Sky. 



Elimination of 
bias. 



two different ways he obtains more independent results 
than if he had moved the spider-webs in the same di- 
rection each time. By turning the box in two opposite 




Self-reliance. 



A Micrometer. 

directions, as he has just done, he also tends to elimi- 
nate a certain amount of personal bias, which would not 
be eliminated if he always turned the box in the same 

direction. He does not 
take many measures of 
the same double star on a 
given night, but prefers 
to take a few on each of 
I several nights, thi n k i n g 
that he will thus secure 
greater independence, 
and consequently a higher 
degree of accuracy in the 
final result. 

Practical astronomical 
work develops self-reli- 
who has been accustomed 
throughout his mathematical course to work examples 
with the expectation of obtaining answers which agree 




-Third Position of the 
Spider-webs. 



ance. A college student, 



The Astronomer. 



125 



Conceit. 



with those given in the text-books, finds that there are 
no ready-made answers to the problems which a course 
in practical astronomy presents for solution. Should 
he become an astronomer, it will only be after he has 
learned to say to himself, ' ' This result is right because 
I have worked it out with care, and know what I am 
about. ' ' 

Such words suggest conceit, but few classes of men 
are less conceited than original investigators. A sciolist 
may be extremely 
puffed up. A genu- 
ine man of science, 
whose investigations 
bring him to the fron- 
tiers of knowledge, 
finds so many un- 
explored lands lying 
before him and so 
many apparently y, 

impassable mountain 
ranges in his path 
that he is forced into 
an habitual attitude 
of humility. There FlG 6l 
come to mind the oft- 
quoted words of Sir Isaac Newton : "I know not 
what the world may think of my labors, but to myself it 
seems that I have been but as a child playing on the sea- 
shore ; now finding some pebble rather more polished, 
and now some shell rather more agreeably variegated 
than another, while the immense ocean of truth extended 
itself unexplored before me." 

Finally, what shall we say about the personal habits personal 
of astronomers? Is an astronomer a good neighbor? 




-Seth C. Chandler, of Cam- 
bridge, Mass. 



126 



A Study of the Sky 



Temper. 



A literary 
ebullition. 



Usually he is ; in rare instances he is not. To be sure, 
he often comes home pretty late, but he has no difficulty 
in fitting his latch-key into the proper place ; he has not 
been at a carousal. Sobriety is his habit. Bleared 
eyes and unsteady hands are not fit for astronomical 
work.* 

He is usually quiet, and not easily roused. In the 
comparative seclusion of his observatory he gains a 
habit of calmness. To arouse whatever is evil in his 
nature you have but to interrupt him while he is intent 
upon some observation. On such an occasion he is 
likely to be short-tempered and sharp of speech. He 

reasons thus : "A 

+—*>$$ ■ business man would 

JpP^ 9| treat me with scant 

JH courtesy if I asked 

him to give up his 

business hours for 

my pleasure. Why 

should he not realize 

that I have business 

hours as well as he ? " 

On occasions when 

he feels compelled to 

yield, he sometimes 

does curious things. 

Fig. 62.— Sherburne W. Burnham, of the In One of the observ- 
Yerkes Observatory. . ...... 

ing books in the 
archives of an American observatory is found this 
sentence, written at such a time : "Visitors who come 
on working nights and interrupt a series of observations 




* It is related of an assistant in an English observatory' that once, when on a 
visit to this country, he was found lying in a gutter, in a state of intoxication. 
A policeman shook him rudely, and asked, "What are you doing here?" 
'' Observing, sir," was the sententious reply. 



The Astronomer. 127 



are undoubtedly parietosplanchnic Lamellibranchiates, 
afflicted severely with psittaceous psychopannychism." 
Such nonsense must have been an effectual safety-valve 
for the writer's feelings. On a similar occasion another 
astronomer rushed from the dome-room into an adjoin- An attack, 
ing apartment, seized a poker, and paced furiously up 
and down past the base-burning stove ; a fresh hole 
gaped in the isinglass whenever he went by. 

Ordinarily, however, the director of an observatory 
treats visitors who come at proper times with the utmost 
courtesy, and is best pleased if they rain upon him a 
shower of questions about his instruments or the celestial 
objects in view. 



CHAPTER VIII 



A GREAT TELESCOPE. 



" Through thee will Holy Science, putting off 
Earth's dusty sandals from her radiant feet, 
Survey God's beauteous firmament unrolled 
Like to a book new- writ in golden words, 
And turn the azure scroll with reverent hand, 
And read to man the wonders God hath wrought.'* 

— A. V. G. 



Roger Bacon. 



Hans 
Lippershey 



Galileo. 



Failures. 



The great telescope of to-day has been evolved 
during the past three centuries by a slow process of 
growth. Before its actual invention many men had 
ideas about the possibility of making an instrument 
which would make distant objects appear near at hand. ■ 
Roger Bacon, who died in 1294, stated that transparent 
bodies could be made in such forms and placed in such 
combinations as to magnify objects. But he never con- 
structed a telescope, for he ascribed to such an instru- 
ment some properties which it does not possess. 

In 1 60S Hans Lippershey, a resident of Middleburg, 
Holland, invented the telescope. During the ensuing 
year. Galileo heard of the new invention, and reinvented 
the instrument. He made several small telescopes, the 
most powerful of which magnified thirty-three diameters, 
and revealed the spots on the sun, the lunar mountains, 
the moons of Jupiter, and the phases of Venus. 

Slight progress was made during the next hundred 
years. Men failed to get clear, sharp images of objects, 
no matter how accurately they ground the lenses of 

128 



A Great Telescope. 



129 



their telescopes. Even the immortal Newton was foiled. Newton foiled. 
When he discovered that white light was dispersed 





Fig. 63. — The Yerkes Telescope at the Columbian Exposition. 

into a number of different colors by being passed Dispersion of 
through a prism, he also found that passage through a llght ' 



130 



A Study of the Sky 



Newton's 
reflector. 



Lord Rosse's 
reflector 



Silver on glass. 



lens affected it in the same way. Believing that the 
dispersed rays could not be reunited, Newton gave up 
all hope of perfecting Galileo's form of telescope, and 
turned his attention to making concave mirrors, which 
reflected the light to a focus without dispersing it. 
Newton's first reflecting telescope was six inches long, 
and was equipped with a mirror one inch in diameter. 
So successful was the performance of this pigmy that he 
made a larger one, which is now in the possession of 
^~ the Royal Society of 

/ London, and bears 

this inscription: 
' ' The first reflecting 
telescope, invented 
by Sir Isaac Newton, 
and made with his 
own hands. 

As the years rolled 
on, reflecting tele- 
scopes of larger and 
larger sizes were 
made, until at last 
Lord Rosse's levia- 
than, which has a 
mirror six feet in di- 
ameter, was mounted at Parsonstown, Ireland, fifty years 
ago. No other reflector of equal size has yet been con- 
structed. Its mirror was made of polished metal. It is 
now customary to make the mirror of glass, and to coat 
it with silver. 

Such telescopes offer special advantages for photo- 
graphic and spectroscopic work, since the light which 
impinges upon a mirror suffers no dispersion, as it 
would if passed through a lens. 




Fig. 64. 



-Alvan G. Clark, Optician, of 
Cambridge, Mass. 



A Gi'eat Telescope 



131 



Since reflectors are little used in this country, we 
return to the history of the common form of telescope, 
which is called a refractor. The name refractor arises 
from the fact that rays of light, in passing through a 
lens, are bent, or "refracted." 

We have noticed that Newton thought it impossible 
to reunite the rays of various colors which were scat- 
tered in passing through his lenses. But early in the 
eighteenth century a well-to-do countryman of his, Mr. 
Chester Moor Hall, was struck with the fact that the 
human eye, which contains more than one refractive 
medium, produces images practically free from obnox- 
ious color fringes. By combining two lenses of different 
kinds of glass he reunited the dispersed rays pretty well. 
Being a gentleman of leisure, he took no particular pains 
to follow up his discovery, and the credit of it was soon 
given to Mr. John Dollond, an optician, who experi- 
mented successfully along similar lines and published an 
account of his work in 1758. 

A new difficulty of the first magnitude now arose. 
Good discs of glass more than three and a half inches in 
diameter could not be procured. In vain the French 
Academy offered prizes for larger discs ; the best 
chemists were baffled. But the battle is not always to 
the strong. From 1784 to 18 14, Guinand, a poor Swiss 
watchmaker, toiled with dauntless industry, overcoming 
one obstacle after another, until he succeeded in produ- 
cing glasses eighteen inches in diameter. 

The manufacture of a large disc of optical glass* 
requires the utmost carefulness, as well as a high degree 

* There are now only three firms in the world which have made very large 
lenses, Chance & Co., of Birmingham, Mantois of Paris, and Schott & Co., of 
Jena. Schott & Co. now produce a number of different kinds of glass, and a 
large amount of experimentation is going on, in an endeavor to find combina- 
tions of lenses which will give more satisfactory results than the time-honored 
• combination of a lens of crown glass backed up by another one of flint glass. 
Professor Hastings, of Yale, has been successful in such researches. 



A refractor. 



Color fringes. 



A new diffi- 
culty. 



132 



A Study of the Sky. 



The materials 
melted. 



The stirring. 



The furnace 
luted. 



of technical skill. Nineteen trials were made for one of 
the lenses of the 36-inch Lick object-glass, before suc- 
cess was attained. 

A pot made of very pure clay is heated to a high 
temperature, and gradually filled with a batch of the 
raw materials. After the batch seems to be thoroughly 
melted a portion of it is taken out and examined, to see 
if any unmelted particles of silica remain, or if there are 
minute air-bubbles, which have not been expelled by 
the heat. 

Should neither of these defects be discovered, the 

melted glass is 
stirred with an iron 
rod, the lower 
portion of which is 
covered with clay. 
The stirring is con- 
tinued for two or 
three hours, until 
the cooling glass 
resists further ma- 
nipulation. The 
two workmen, who 
swelter in the furnace heat while executing this opera- 
tion, must not allow the stirrer to touch the pot ; for 
bits of clay might be ground off and mixed with the 
glass. 

The glass is reheated, stirred a second time and even 
a third time, and returned to the furnace. Every open 
place in the furnace is stopped up, so that no air may 
gain admittance, and the whole is allowed to cool for 
several days, that it may not crack. A rapid cooling 
would cause it to be shattered into small fragments. 
When the cooling is finished the glass is examined, 




Fig. 65. — Lump of Optical Glass. 



A Great Telescope. 



33 



.-■^- - v 




and any defects which may be apparent are ground 
away, or sawed off. An imperfect spot near the center 
of the disc may be sawed out, if the chunk of glass is 
not sawed clear 
through. 

The accompany- 
ing figures show 
the block of glass 
from which the 
crown disc of the 
forty-inch Yerkes 
telescope was ob- 
tained. Fig. 65 is 
the original lump. 
Fie. 66 shows it FlG - 66,— The Lump Cut down. 

after some imperfections have been sawed off. The 
lump is now to be molded into the shape shown in Fig. 
67. The glass is put into a mold, which is placed in a 
special furnace and heated very slowly. At last the 

glass softens and 
adapts itself to the 
shape of the mold. 
The temperature is 
lowered to about 
1 ,200° Fahrenheit, 
and every opening 
in the furnace 
stopped up ; after 
an exceedingly 
slow and careful 

Fig. 67.— The Lump Molded. COoli n o- the ten- 

sided block is removed and examined. Fresh imper- 
fections are discovered and cut away, as Figs. C8 and 
69 testify. The defects may be of such a nature that 



Imperfections 
cut out. 




A forty-inch 
disc. 



134 



A Study of the Sky. 



Bubbles. 



Striae. 




Internal strain. 



the disc must be reheated and molded again, but if too 
many annealings are attempted, the glass may lose its 
transparency. After months of labor the original shape- 

less mass is re- 
duced to a beauti- 
ful circular disc. 

A few small bub- 
bles, or bits of grit, 
while they mar the 
appearance of a 
disc, have no per- 
ceptible delete r- 
i o u s effect in a 
finished lens. They 

Fig. 68.— The Lump after Further Cutting, nrevent the DaS- 

sage of a certain minute quantity of light, and theo- 
retically injure the perfection of the image of an object 
seen through the lens. 

When a careful test is made ' ' striae, ' ' or veins, may be 
found in the in- 
terior of the lens : 
should these be 
numerous or pro- 
nounced the lens 
must be rejected. 

The glass may 
have passed 
through all these 
tests and yet be 
worthless. If the 
process of cooling 

was not conducted with sufficient care 
have solidified in a state of dangerous internal strain. 
To test for this the glass is laid upon a piece of dark 




F* 



—The Lump Cut Down Still More. 



the glass may 



A Great Telescope. 



135 



cloth, in some place where there is suitable light, and 
examined by a Nicol's prism. If a pronounced dark 
cross is seen in the glass, the internal strain is too great, 
and the glass must not be used for a telescope. 

The glass-founder has now finished his part of the The optician's 

5 r work. 

work, and the 
disc, if sufficiently 
perfect, is turned 
over to the op- 
tician, who is to 
fashion its curves 
so accurately that 
the rays of light 
from a distant 
star may be con- 
verged by it to a 
point which can 
be covered with 
a spider's web. 

The rough grinding is done with a cast-iron tool, 
similar in appearance to the one lying on the floor in the 
illustration (Fig. 70). If a convex surface is to be pro- 
duced on the glass, the tool is hollowed out and made 
of the proper degree of curvature. The usual grinding 
material is emory, which is placed between the tool and 
the glass. A better material is obtained by driving a 
blast of air into melted iron. A cloud of minute 
particles of iron is blown out ; being chilled by contact 
with the air they settle down as a very fine powder. 

After the lens has been brought nearly to the proper 
shape it is placed upon the machine shown in Fig. 
70 to be brought to its proper form by polishing. 
The tool, which lies upon the lens, is similar to the 
former one, except that its face is composed of squares 




Fig. 70. — Machine for Polishing Lenses. 



The grinding. 



The polishing. 



136 



A Study of the Sky. 



The testing. 



An artificial 
star. 



of pitch, instead of squares of cast-iron. The lens lies 
on a table which turns slowly. The tool is moved by 
two wooden rods, each of which is driven by a crank at 
its further extremity ; the cranks are of different lengths, 
and turn at widely different rates. So complicated is 
the motion that the tool never describes the same path 
twice. When the surface has been brought to a brilliant 
polish, the lens appears to be finished. 

But the most difficult part of the process is yet to 
come. The surface, which looks perfectly spherical, is 




Fig. 



-Alvan Clark's Workshop. 



probably too high in certain regions and too low in 
others ; these inequalities must receive attention. A 
spherometer which will measure 5W00 of an inch is too 
rude to measure them. The lens is set up on edge in a 
special testing room, where the temperature is not 
subject to sudden variations ; light from a lamp shining 
through a small hole is sent through the lens, and 
impinges on a mirror, which reflects it back again 
through the glass to the eye of the optician. To him 
the entire lens appears to be aflame with light. If it is- 



A Great Telescope. 



137 



Inequalitise. 



not uniformly bright all over, its shape is not perfect. 
Imperfect portions cause dark spots in the midst of the 
general brightness. Perhaps some part of the surface is 
too high and must be polished down ; perchance it is 
too low, and the rest of the surface must be brought 
down to it. From the testing room to the polisher and 
back again the lens 
must go, till the op- 
tician is satisfied 
with its perform- 
ance. At times the 
operator rubs down 
some protuberant 
portion with his 
hand. 

If the lens is 
touched with one 
fi n g e r for a few 
seconds, during the 
process of testing, 
the heat thus com- 
municated to the 
lens raises an intol- 
erable lump in it, 
which will not dis- 
appear till that por- 
tion of the glass has 
cooled again. A zone which is elevated three or four 
millionths of an inch must not be neglected. 

The final shaping of the lens ordinarily involves the Final touch< 
expenditure of so much time that the cost of rubbing off 
a given quantity of the material is one thousand times as 
great as the cost of taking off an equal quantity by the 
first process of rough grinding. 




Fig. 72. — John A. Brashear, Optician, of 
Allegheny, Pa. 



138 



A Study of the Sky. 



Placed in a cell. 



The mounting. 



The earth's 

rotation 

counteracted. 



An odd axis. 



The finished object-glass is put into a cast-iron cell ; 
the edges of the two lenses composing the object-glass 
do not touch the cast-iron ; each of them rests against a 
silver surface on the inside of the cell ; otherwise a little 
corrosion of the iron might damage the glass. The cell 
is then ready to be fastened to the steel tube of the 
telescope. 

The instrument maker has an important work to per- 
form before the great lens can be set 

" Like a star upon earth's grave and cloud-encircled brow." 

He must make such a mounting that the telescope can 
be readily directed to any point in the sky ; further- 
more, the telescope must move automatically in such a 

way that a star may be 
kept in the field of 
view for hours. 

Since the earth ro- 
tates, and carries the 
telescope with it, the 
latter, if directed toward a given star, at any instant, 
will point in quite a different direction a minute after- 
ward. The mechanician must therefore counteract the 
rotation of the earth. 

For purposes of explanation it is best to consider the 
earth as fixed and the celestial sphere as rotating about 
an axis drawn from the north celestial pole to the south 
celestial pole. This conception has already been pre- 
sented in Chapter II. Imagine this axis to be a wooden 
shaft six inches in diameter, rotating steadily, making 
one turn in twenty-four hours, and carrying the celestial 
sphere with it. 

If a lath be nailed to this shaft in such a position that 
it points to Sirius, it will continue to point toward Sirius 





Fig. 73. — The Two Lenses of an Object- 
Glass. 



A Great Telescope. 



139 



day after day, as the shaft and sphere rotate together. 
This is the fundamental idea upon which the mechan- A 9 teei shaft, 
ician seizes. He quickly perceives that he can set up a 
short shaft of steel, 
which shall point to 
the north celestial 
pole, and resemble a 
section of the wooden 
shaft which we have 
been considering. By 
s u i table mechanism 
he can rotate the steel 
shaft once in twenty- 
four hours. Then if 
he can attach the tel- 
escope to this shaft 
in such a way that it 
can be pointed in any 
direction, the prob- 
lem is solved. 

The fundamental 
shaft which points 
toward the celestial 
poles, and is parallel 
to the earth's axis, is 
called the polar axis, 
and is shown on top 
of the pillar in Fig. 
74 ; it is below the 
telescope and parallel 
to it. To the upper 
end of the polar axis is fastened a long "sleeve," at 
right angles to it. Inside this sleeve turns another axis, hunting?"* 1 
called the declination axis, at the lower end of which a 




Fig. 74.— An Equatorial Telescope. 



140 



A Study of the Sky 



Ingenious 
contrivances. 



Accurate 
workmanship. 



Various 
materials. 



lamp is shown in the figure. The declination axis carries 
a heavy weight, to balance the weight of the telescope, 
so that the entire structure may be nicely poised on the 
polar axis. The telescope is fastened to the declination 
axis, and is at right angles to it. On each axis there is 
a graduated circle ; by these the astronomer sets the 
telescope so that it points toward any object whose right 
ascension and declination are known. The clock-work 
for rotating the polar axis lies under it, and is driven by 
a weight concealed in the hollow pillar which supports 
the instrument. 

A large instrument of this kind is very complicated, 
and fairly bristles with ingenious contrivances to facili- 
tate the work of the exacting individual who is to use it. 
When an astronomer's eyes first rest upon a great 
telescope, with which it is to be his good fortune to 
storm the sky, his sensations are of the liveliest charac- 
ter. The mass of steel, iron, and brass which confronts 
him speaks eloquently of the patient ingenuity of the 
mechanician who calculated the form and dimensions of 
each of the hundreds of pieces of metal which are joined 
in the intricate mechanism, and subordinated them all to 
one great purpose. 

It also tells of the painstaking care of many skilful 
workmen, who have toiled thousands of hours perfect- 
ing the teeth of the gears, polishing the pivots and 
bearings, making the various screws true, and fitting all 
together, to form a harmonious whole. 

Not only must the different parts be correctly pro- 
portioned, but each must be made of the proper 
material. Steel of various degrees of hardness, cast- 
iron, wrought-iron, brass, copper, lead, phosphor- 
bronze, silver, German silver, nickel, hard rubber, 
wood, carbon, glass, vegetable fiber, and even spider- 



A Great Telescope. 



141 



webs all occupy their proper places. At some points 
friction is relieved by ball-bearings ; at others by friction Fricti 
rollers ; at still others friction must have full play. 




Fig. 75.— The Chamberlin Telescope of the University of Denver. 

The tons of metal which compose the moving parts of Elec 
the great Yerkes telescope are moved in any direction, 
swiftly or slowly, by means of electric motors. The 



trie 

motors. 



142 A Study of the Sky. 

astronomer presses the button, the motor fulfils his 
bidding. 

Fig. 75 shows a large telescope ready for work. The 
its t h 1 ome° pe in P n l ar g° es through the floor without touching it, and 
rests on a stone pier below. Near the bottom of the 
pillar are two hand-wheels, by means of which the tele- 
scope can be moved quickly into any desired position. 
Above them is a box containing clock-work which 
indicates the right ascension and declination of any 
object at which the telescope is pointing. Through a 
glass door in the uppermost section of the pillar one 
may see the driving clock. The declination axis is 
behind the tube. The observing platform, which slides 
up and down along an inclined runway, is shown at the 
left. The overarching iron dome rests upon anti- 
friction wheels, which are on top of the stone wall. 



CHAPTER IX. 

THE ASTRONOMER'S WORKSHOP AND SOME OF HIS 
TOOLS. 

" Go to yon tower, where busy science plies 
Her vast antennae, feeling thro' the skies ; 
That little vernier, on whose slender lines 
The midnight taper trembles as it shines, 
A silent index, tracks the planets' march 
In all their wanderings thro' the ethereal arch, 
Tells through the mist where dazzled Mercury burns, 
And marks the spot where Uranus returns." 

— Holmes. 

An astronomical observatory is conspicuous among 
surrounding structures by its unusual appearance. One 
or more domes surmounting it catch the eye at once. 
There are long narrow doors in the walls and shutters 
on the roof, which arrest attention. Fig. 76 is a repre- 
sentation of an observatory. 

First as to the site. The location is usually not a 
matter within the astronomer's control ; he is fortunate 
if he is even allowed to plan the building, so as to 
adapt it to the purposes to which it is to be devoted. If 
he had his choice of location, he would be likely to 
choose a considerable elevation. 

A mountain top would seem most suitable were it 
available ; but experience shows that such is not usually 
the case. The advantage is that the observer is above 
quite a thickness of atmosphere, so that the stars shine 
out more clearly, and faint objects are more distinctly 
visible. But the disadvantages are many. On a moun- 

143 



An observatory. 



Its site. 



A mountain. 



144 



A Study of the Sky 



tain top the air is almost always in motion ; warm 
currents rush up the sides of the mountain, and cooler 
air descends. The expansion of the warm and vapor- 
laden air, which comes from below, chills it, and pro- 



Obtrusive 
currents of air. 



The environs of 
a citv. 




76.— The Yerkes Observatory, 



or even clouds, which 



hang about the 



duces mists 
summit. 

Even when no mist forms, whirling currents come 
between the telescope and the celestial object toward 
which it is pointed. The light from the object, in pass- 
ing through these changing currents, is bent hither and 
thither, so that the object appears to dance, and to 
be distorted ; no satisfactory view of it is possible. 
Furthermore the wind shakes the telescope itself, and 
renders accurate observations out of the question. It is 
generally admitted that an ideal site is an elevated 
plateau ; the farther it is from a mountain range the 
better ; a dry atmosphere is also considered advan- 
tageous. 

Where circumstances limit the location to the neigh- 
borhood of some city, a study of the prevailing winds is 
made, so that the evil of the city's smoke may be 
minimized. A spot of ground embracing a few acres, 
so that other buildings may not be built too near the 



The Astro7iomer s Workshop. 145 

observatory, and commanding a fair sweep of the 
horizon, is sought. It is advisable to avoid proximity 
to railroads, because of the earth tremors caused by the 
passage of heavy trains. 

When the site has been chosen and the instrumental 
equipment determined upon, the building is so planned 
as to furnish a suitable home for the instruments, and 
working quarters for the astronomer. The building 
shown in the illustration (Fig. 77) faces southward 
because the large telescope under the dome is chiefly 
used for observing objects in the south, east, or west, 
and is not often pointed northward. Were the building 
turned around, the observer would have to look over 
some portion of the roof most of the time. From the 
roof, which has been heated during the day, arise cur- 
rents of warm air which would disturb telescopic vision. 



r~ 



t 




The building. 



Fig. 77. — The Chamberlin Observatory. 

To avoid these as much as possible the wings of the 
building are set back. 

The meridian circle, the instrument next in im- 

The transit 

portance, is now to be provided for. Shall it be in the room. 
-east wing or in the west ? If it is put in the west wing, 



146 



A Study of the Sky. 



The clocks. 



Temperature 
and humiditv. 



Special 
supports. 



which is heated up by the afternoon sun, observations 
in the early evening will be vitiated by the currents of 
warm air rising all about it. The east wing, on the 
other hand, is largely protected from the sun in the 
afternoon, being in the shadow of the rest of the build- 
ing. This instrument is therefore installed in the east 
wing ; a continuous slit is cut in the roof and in the 
north and south walls, so that the telescope may survey 
the entire meridian from the north point of the horizon 
up to the zenith, and down to the south point. When 
the instrument is not in use the slit is closed by doors. 

The clocks are next to be suitably housed. Shall 
they be put in the west wing ? By no means. For the 
heat of the afternoon sun would cause them to change 
their rates. Fine clocks are supposed to be so con- 
structed that changes in the temperature will not cause 
them either to gain or to lose. But no clock has yet 
been made which will not change its rate under varia- 
tions of temperature. Why, then, shall they not be 
placed in the deep basement underneath the tower, 
below the surface of the ground, where the thermometer 
will probably not vary 5 a day, in ordinary weather? 
In that location there will be another foe to fight ; for a 
cellar, even though it be surrounded by a stone wall two 
feet thick and have a cement floor, is damp. The 
delicate mechanism of the clocks will suffer from this 
cause. The clocks must not stand on the floor or be 
hung upon wooden partitions. Special piers must be 
built to support them, unless there is some other 
adequate provision for them. 

In order to avoid changes of temperature a portion of 
the round tower is partitioned off, on the main floor. 
The space shown in Fig. 78 is so selected that no wall 
of the clock-room, except a very short length, where 



The Astronomer s Workshop. 



147 



two windows are, is an outside wall of the building. 
These two windows are made double, and covered with 
wooden shutters. Thus both the sun's rays and the 
storms of winter are guarded against. If the clocks 
were hung on the stone wall which partly bounds the 
room, the turning of the dome, which rests on this wall, 




The clock- 
room. 



Fig. 78.— Main Floor of the Chamberlin Observatory. 

might jar them a trifle. Therefore the great pier in the 
center of the tower is utilized. Stout beams are built 
into the pier, and project through the thin partition into 
the clock-room ; the beams do not touch the partition, 
for in that case the vibrations of the floor, as people 
walk about on it, would shake the clocks. 

The west wing contains the study of the astronomer. The study. 



148 



A Study of the Sky. 



The basement. 



Foundations 
and floors. 



The upper 
storv. 



No heat. 



He does not care for the heat of the long summer after- 
noons, if the instruments are protected from it. 

In the basement arrangements are made for the heat- 
ing plant, which, if one has plenty of money to spend, is 
a hot-water system ; also for a photographic dark-room, 
battery-room, janitor's quarters, storeroom, and work- 
shop. A good carpenter's bench and a small kit of 
tools are needed. If the observatory is a large one, a 
lathe and other machines for working metals are a part 
of the equipment. Quite a little of the basement is oc- 
cupied by the piers on which the instruments rest. 

The foundations of these are sunk pretty deep, the 
depth depending upon the character of the soil. A 
gravel bed makes an excellent foundation ; rock or hard 
clay is also satisfactory, except that they readily trans- 
mit vibrations arising from the passage of railroad trains 
within half a mile, or heavy traffic in a neighboring 
street. The floors must not touch any of the piers, for, 
in that case, the vibrations caused by human footfalls 
will be communicated to the piers and thus to the 
instruments.* 

In the upper story of the observatory the principal 
room is the dome-room, the home of the great telescope. 
On a level with the floor of this room is an extensive bal- 
cony from which one can glance at all parts of the sky. 
Two or three small rooms adjoin, where various attach- 
ments of the telescope are kept, and where the observer 
may occasionally warm himself on a bitter night. 

It is not practicable to heat the dome-room, for the 



* Before the telescope of the Chamberlin Observatory was installed, the floor 
of the dome-room was shored up on the great pier, so that it might not sag 
when the various parts of the telescope were laid on it, preparatory to being 
put together. After the telescope was mounted, the props were forgotten for 
a time, and every star under observation danced about in a most dishearten- 
ing manner, as people walked about the room. In a few days the props were 
remembered and knocked out. The trouble ceased at once. The stone pier 
which had been so shaken weighs 320 tons. 



The Astronomer 's Workshop. 



149 



heated air would escape through the slit, when the dome 
shutter was rolled off. Nor is it allowable to experiment 
in this direction, because a current of warm air rising in 
front of the large glass would cause the stars to appear 
blurred and to dance about in such fashion that no satis- 
factory views of them could be had. 

Domes more than thirty-five feet in diameter are built Domes# 
of iron. They are made as light as is consistent with a 
proper degree of rigidity, and are covered with heavy 
galvanized iron. Great care is taken to mount them in 
such a manner that they will rotate with ease. An 
astronomer whose strength has been exhausted by turn- 
ing an unmanageable dome is in no physical condition 
to manipulate a delicate instrument, the smallest reading 
of which corresponds to a distance of sothjtf of an inch. 

Where a good current of electricity and a small elec- 
tric motor are available, the observer has but to touch a a rising floor 
push button, and the dome revolves. For very large 
telescopes, the floor of the dome-room is made of iron, 
and is raised or lowered by powerful machinery, which 
may be started and stopped by pressing a button. 

Some of the astronomer's tools are so important and 
so common that we must examine them. The great 
telescope which was described in the last chapter is 
much too cumbersome to be used in the most refined in- 
vestigations for determining the right ascensions and 
declinations of "fundamental stars." The instrument 
used for this purpose is comparatively small, extremely 
rigid, and so mounted that it can view a celestial object 
only when the latter is near the meridian. 

Fig. 79 shows that the instrument consists of a tele- 
scope, which is perpendicular to a horizontal axis. The 
axis points east and west and terminates in two cylin- 
drical steel pivots, each of which rests in a wedge-shaped 



Some of the 

astronomer's 

tools. 



150 



A Study of the Sky. 



The graduated 
circles. 



Measurement 
of angles. 



metal bearing called a V,* from its resemblance to that 
letter. These bearings are fastened very securely to two 
substantial piers, generally of stone. 

Upon the axis are mounted two circles, one, at least, 
of which carries a band of silver, on which fine marks, 
technically called ' ' divisions " or " graduations ' ' have 
been cut with the utmost accuracy. If each division 

represented a 
degree there 
would be 360 of 
them around 
the entire cir- 
cle. Usually 
there is a grad- 
uation for each 
five minutes of 
arc; as five min- 
utes constitute 
one twelfth of a 
degree, there 
are 12 x 360, or 
4,320 gradua- 
tions on the 
circle. 

If the tele- 
scope, wnicn is now pointing upward, were turned so 
as to point downward, the graduated circle would turn 
with it, and the angle through which the telescope was 
turned could be measured by means of a suitable fixed 
pointer placed close to the silver graduations. If the 
pointer were opposite the io° mark on the circle when 
the telescope was pointing directly upward, it would be 
opposite the mark for 190 when the telescope pointed 

* This bearing is commonly referred to as a " wye." 




b\o. 79.— A Meridian Circle. 

which is now pointing upward, 



The Astro7io7?ter' > s Workshop. 151 

straight down, the circle having been turned just half 
way round. Instead of one pointer there are usually 
four ; the silver graduations are so fine that they cannot 
be well seen without a magnifying glass ; the pointer 
must therefore be very fine, and the spider is called 
upon to furnish it. 

The spider-web, which is to serve as a pointer, is 
placed inside of a microscope, which is sighted at the T ^e reading 

1 _ 1 "^ microscopes. 

silver circle. To insure great accuracy in reading the 
circle four microscopes are frequently employed. They 
are shown in Fig. 79, being fastened to a metal drum, 
which rests on top of one of the piers. On looking 
through one of the microscopes one sees the spider- 
web, and also the magnified divisions on the circle. At 
the outer end of each microscope a little box is placed ; 
this contains a measuring instrument called a microme- 
ter. If the spider-web does not appear to coincide 
with one of the graduations on the circle, its distance 
from the nearest graduation is measured with the mi- 
crometer. The silver circles are usually read to the 
nearest tenth of a second of arc. If such a circle be 
ninety inches in circumference, a tenth of a second is 
only titooo of an inch. 

Standing upon the horizontal axis of the instrument is 
a metal frame which supports a delicate level, the sensi- 
tiveness of which is astonishing. Suppose that two 
points on the level tube, one eighth of an inch apart, 
are in the same horizontal plane at a given instant. If 
by some movement of the instrument one of the points 
is raised a millionth of an inch above its neighbor, the 
level bubble will move. 

A peep through the eyepiece of the telescope reveals 
a forest of black lines ; at night, when lit up by a special 
lamp, they appear as a system of golden wires. In Fig. 



The level. 



The reticle. 



I.S2 



A Study of the Sky. 



The celestial 
meridian. 



A surveyor's 
transit. 



80 are nine parallel wires, and one at right angles to 
them. Eight are arranged symmetrically with respect 
to the middle wire. They come from the spider's loom ; 
woe to the luckless wight who accidentally touches 
them, or blows upon them ! They are in the focus of 
the telescope, close to the observer's eye, inside of the 
tube. If the telescope be directed to the heavens on a 
clear night, star after star will pass through the field of 
view, marching across one vertical wire after another, 
moving parallel to the horizontal wire. 

When a star is just crossing the middle wire, it is on 
the celestial meridian of the place of observation, if the 
instrument is in perfect adjustment. Let us stop a mo- 
ment and think out the reason why a star is on the 

meridian when it is on 



this middle wire. 

Consider a surveyor's 
transit which he carries 
about and sets up on 
its tripod whenever he 
wishes to make any 
measurements. In it 
there are two cross 
wires, one horizontal, 
the other vertical. If 

Fig. So.— The Spider-webs. he wishes tO Sight at the 

top of a church spire he moves his telescope until the 
tip of the spire appears to lie on the intersection of the 
cross wires. At that instant a straight line drawn from 
the top of the steeple through the center of the object- 
glass of the telescope strikes the point where the two 
wires cross each other. This line is called the sight-line 
of the telescope. 

Returning to the meridian circle we see that its sight- 




The Astronomer 1 s Workshop. 



*53 



line, which is a line drawn from the center of the object- 
glass* to the point where the horizontal and central ver- 
tical wires meet, is perpendicular to the horizontal axis. 
Let us point the telescope at some house miles away to 
the southward. Since the horizontal axis points east 
and west, the sight-line, which is perpendicular to it, 
must be pointing due south. If a chimney of the house 
appears to lie 
upon the middle 
wire the chimney 
is due south of 
the instrument. 
Passing by the 
house we pro- 
long the sight- 
line to the celes- 
tial sphere, which 
it strikes at the 
south point of the 
horizon. 

We g ently 

take hold of the FlG - 81.— The Spire on the Cross Wires. 

telescope and pull the eye-end down ; as it turns on the 
horizontal axis the object-glass rises, and the sight-line 
traces a line on the celestial sphere. Farther and far- 
ther upward the line is traced on the sky till it reaches 
the zenith. As we go on, the circle which we have 
been tracing runs down from the zenith to the north 
point of the horizon. The telescope is now horizontal, 
and pointing northward. We continue revolving the 
telescope in the same direction ; the eyepiece rises and 
the object-glass falls, while the sight-line is cutting into 
the earth's surface, tracing upon it the terrestrial merid- 

* The large glass at the upper end of the tube. 



The meridian 
circle again. 




The telescope 
is revolved. 



154 



A Study of the Sky. 



Mechanical 

perfection 

sought. 



Perfection 
impossible. 



ian of the place of observation. When the telescope 
finally reaches its original horizontal southward-pointing 
position, the sight-line has traced the celestial meridian 
on the sky, and the terrestrial on the earth. If the 
celestial meridian were visible as a fine gold thread lying 
on the celestial sphere, and one tried to look at it with 
the meridian circle, it would be concealed from view, 
being behind the central spider-web. Therefore, at the 
instant when any star appears to be crossing the central 
spider-web, it is on the meridian. 

Thus far we have considered the meridian circle as an 
ideally perfect instrument. True it is that the mechan- 
ician has exhausted the resources of his art when he has 
made a first-class meridian circle. He has striven to 
make the pivots at the ends of the axis of the same size 
and exactly round. The telescope has been set at right 
angles to this ; the object-glass and spider-webs have 
been inserted with the utmost care. Upon the gradua- 
tions of the silver circle weeks of the most painstaking 
labor, coupled with the most scrupulous care, have been 
lavished. The microscopes with which the circle is read 
have been constructed with an eye to perfection. The 
interior of the glass level-tube, which is to test the hori- 
zontality of the axis, has been ground to the proper 
curvature, and fastened to its supporting frame in such a 
way that changes of temperature will not cause the tube 
to be pinched or sprung. The mason has endeavored 
to set the supporting piers so solidly that nothing short 
of a miniature earthquake will disturb their positions. 

The astronomer views the finished work with the ad- 
miration which every one must have for any piece of 
mechanism which represents the utmost of human skill. 
But the instrument, which is to the eye of the body a 
thing of beauty, is to the mind a mass of imperfections. 



i56 



A Study of the Sky. 



Flexure. 



Errors of 
graduation. 



Level errors. 



Movements of 
the ground. 



A difficult task. 



The pivots on which the instrument revolves are of 
unequal sizes, and neither of them is round. For this 
reason alone the sight-line, instead of tracing a perfect 
circle on the sky, traces a gently waving line. The 
axis, which is apparently amply able to support the 
light telescope, bends a trifle under its weight ; per- 
chance one half of it bends more than the other half. 
The telescope tube flexes under the weights of the 
object-glass and of the eye-end. Changes of tempera- 
ture and other causes alter the position of the object- 
glass in its cell, and change the direction of the sight- 
line, which passes through its center. 

The exquisite silver circle will cost the astronomer 
many a month of arduous toil. For if he assumes that 
one of the graduations is exactly in the right place, 
almost all of the remaining 4,319 are so far out of their 
true positions that he must determine their errors. As 
we have before stated, he wishes to read as small a 
quantity as ttiWo of an inch, and most of the circle- 
divisions are in error as much as -eowo- of an inch ; some 
of them are over 2W00 of an inch out. The little mi- 
crometers on the microscopes cannot do their small 
duties with sufficient precision. The inner surface of the 
level tube, which has been ground so smooth, is embel- 
lished here and there by a miniature mountain, which 
arrests the free movement of the level bubble. 

The solid foundation on which the instrument has 
been set is continually in motion, shifting the positions 
of the piers by small amounts. Earthquakes are only 
the big brothers of the many small disturbances of the 
earth's crust which are noticed by astronomers alone. 

The observer with a meridian circle has therefore a 
difficult task ; he must manipulate the instrument with 
exceeding care, and must study many of its errors from 



The Astronomer' s Workshop. 



J 57 



night to night, because they continually change in inex- 
plicable ways. His occupation is largely an unrelenting 
chase after errors, which must be determined and taken 
into account. 

A chronograph is considered an indispensable part of 
the instrumental equipment of an observatory. It is 
used, as its name indicates, for noting time. At any in- 
stant when an observer wants to note the time he touches 
a telegraph key, and the chronograph records the time. 
The large cylinder shown in Fig. 83 revolves once a 
minute. If the pen-carriage stood still the pen would 




A chronograph. 



Fig. 



-A Chronograph. 



draw the same circle over and over again on the paper 
which is wrapped around the cylinder. But the mech- 
anism is so arranged that the pen-carriage slides slowly 
from one end of the cylinder to the other. The pen 
therefore traces upon the paper a long spiral line, like a 
screw-thread. When a telegraph operator presses his 
telegraph key the sounder by his side clicks. If a pen 
were suitably attached to the sounder, the pen would 
make a mark on paper. In a similar fashion a notch is 
made in the line which the pen draws on the chrono- 
graph sheet, whenever an observer presses the key. 



The pen- 
carriage slides. 



The record of 

the clock. 



158 A Study of the Sky. 

The clock is equipped with a little device which acts 
like an automatic telegraph key, causing the pen on the 
chronograph to make a notch whenever the clock ticks, 
with the exception of the fifty-ninth second of each 
minute, for which there is no record on the chronograph. 
The omission of this second is a matter of convenience, 
to identify the beginning of each minute. If the ob- 
server notices the time when one of the clock notches 



The time noted. 



Fig. 84. — A Portion of a Chronograph Sheet. 

was made, he can easily tell what the clock read when 
any other notch was made. 

When he sees a star cross a spider-web in the meridian 
circle and touches his key, a notch is made which 
usually comes between two of the clock notches. If it is 
between the notches for g hr - 28 min - 3 sec - and g hr - 28 min -4 sec -, 
the fractional part of a second is estimated from the rel- 
ative distances between the notches. One of the notches 
shown in Fig. 84 was evidently made at g hr - 28 min - 3-4 sec - 
It is much easier for an observer to touch a telegraph 
key at the proper instant than to estimate the required 
time by listening to the ticks of a clock, while his eye is 
occupied at the eyepiece of the telescope. 

The micrometer is used on all kinds of astronomical 
instruments wherever small distances are to be measured 
accurately. It aids in reading the silver circle on a 
meridian circle ; the diameters of planets, the heights of 
mountains on the moon, and the distances of the stars 
are all measured by its help. It is beyond our present 
province to explain how the minute fractions of an inch 
which a micrometer measures are transmuted into miles 
in the celestial spaces, by the alchemy of the mathema- 



The microm- 



The Astronomer 's Workshop. 



159 



tician's art. But we may at least see what the great 
micrometer which is screwed on at the eye-end of the 
Lick telescope looks like, and get a little insight into the 
method of its manipulation. Looking through the eye- 
piece, we shall not be confronted by a forest of spider- 
webs, as in the meridian circle. It will suffice if there 
are but two fixed wires crossing each other at a right 
angle, just as in the surveyor's transit. Besides the fixed 



A great 
micrometer. 




Fig. 85.-— The Lick Micrometer. 

wires there must be one movable one, which is parallel 
to one of the fixed wires. The concealed frame, which 
holds the movable wire, is driven by a fine screw, the a fine 
large head of which is visible at one end of the box. This 
head is graduated so that thousandths of a revolution of 
the screw can be read. If the screw has fifty threads to 
the inch, an entire revolution of it will cause the movable 
spider-web to move -fa of an inch. One hundredth of a 
revolution will cause a motion of 50V0 of an inch. 



i6o 



A Study of the Sky. 



A planet's 
diameter. 




c//SC. 



Distance 
between stars. 



If the diameter of a planet is to be measured, the 
movable spider-web is driven, by turning the screw, 
until the image of the planet in the field of view is neatly 

embraced be- 
tween the two 
parallel spider- 
webs. The read- 
ing of the gradu- 
ated head of the 
micrometer screw 
is taken, and the 
solution of the 
problem is then a 
mere matter of a 
little simple fig- 
uring, which the 
astronomer does 
at his leisure. 

When the ap- 
parent distance 
between two stars 
is to be meas- 
ured, the mi- 
crometer box, 
containing the 
spider-webs, is 
turned till the 
two parallel webs 
stand perpendic- 
ular to a line 

Fig. 86.— Measurement of a Planet's Diameter, joining the Stars. 

At the completion of the measure the spider-webs are 
bisecting the images of the stars, as shown in Fig. 87. 
In reducing observations made with the micrometer 




The Astronomer* 's Workshop. 



161 



no such tantalizing chain of errors is encountered as 
with the meridian circle. If the micrometer screw were 
of even pitch throughout its length, so that each revolu- 
tion of it advanced the spider-web just tu of an inch, all 
would be well. When the irregularities in the screw- 
pitch, which are always very small, have been deter- 
mined, the battle is won. 

If, however, one of the spider-webs is 
accidentally broken, the insertion of a new 
one demands a little skill. The astrono- 
mer cannot sweep down one of the cob- 
webs in the observatory to get a suitable 
wire. House-spiders are too effeminate ; 
their webs are not sufficiently tough, and 
are covered with dust. A big field-spider, 
which successfully copes with an unwary 
grasshopper, binding his struggling victim 
by weaving a shroud about him, produces 
a web that is elastic and tenacious. The 
cocoon, in which are stored hundreds of 
yards of gauzy fiber, is captured. By the 
exercise of a little dexterity a piece of web 
three or four inches long is pulled out and 
placed under a magnifying glass. It 
proves to be too thick, and is rejected. 
Another piece is examined ; curious little 
knots are strung along it. The next piece, 
when held up to the light, is too transpar- 
ent. Soon a fine, smooth, opaque bit of web is discov- 
ered ; it is submerged in a basin of water and stretched 
out, while soaking, so that it becomes finer yet. Inside 
of the micrometer are two fine grooves. One end of the 
web is laid in its groove, with the aid of a magnifying 
glass, and a drop of shellac is dropped upon it ; the 



Errors. 



Fig. 87. — Bisection 
by Spider-webs. 



A broken 
spider-web. 



l62 



A Study of the Sky 



The spectro- 
scope. 



A shower. 



shellac hardens and holds it. It is now stretched taut 
with the utmost care, and the other end fastened in its 
groove ; if it be not pulled with sufficient force, it will 
be baggy and useless. If pulled a trifle too hard, all is 
over in an instant, and the cocoon is explored for a new 
web. 

One more instrument demands attention. It is the 
wonder-working spectroscope, with which substances 
which exist in distant stars are detected, and motions 
otherwise unknown are brought to light. 

White light is a combination of many different colors. 
When the sun shines through a shower of rain, his light 




Fig. 



■Essentials of a Spectroscope. 



Construction 
of the spectro- 
scope. 



is split up in passing through the raindrops, and a rain- 
bow is produced. Many an old lamp, once the glory 
of grandfather's parlor, is surrounded by prismatic 
pieces of glass, which are rich with varied hues, as the 
light shines through them and is dispersed into its 
component colors. 

The spectroscope is a beautiful instrument, in which 
the light is dispersed, and by which it is studied. 
Fig. 88 shows a triangular prism of glass, on each side 
of which a telescope is placed. The eyepiece of the 



Specti 



Experiments. 



The Astro?iomer' s Workshop. 163 

telescope at the right has been supplanted by a brass 
cap, in which there is a long narrow slit. The light 
from an ordinary lamp enters at this slit, impinges upon 
the prism, is dispersed by the prism, enters the telescope 
at the left, and emerges into the observer' s eye. 

The light which entered the narrow slit has been 
spread out into a ribbon which is red at one end and 
violet at the other. Between these colors lie orange, 
yellow, green, cyan-blue, and ultramarine blue. The 
ribbon is called a spectrum. 

Let us now replace the lamp by a spirit lamp, and lay 
some common salt on the wick. The previously color- 
less flame becomes yellow, as the salt burns. Looking 
into the spectroscope we see no longer a colored band, 
but simply a yellow line. When the salt has been 
burned up we try chloride of lithium in the same way ; 
a carmine line appears. A salt of thallium will produce 
a. green line. Burn all the substances together, and all 
the lines are visible simultaneously. 

Again let us look at the yellow line, as the salt is 
being turned from a solid into a gas, in the hot flame of experiments. 
the spirit lamp. Behind the spirit lamp is put a very 
bright white light, which will shine through the hot gas 
into the slit. In place of the bright line produced by 
the glowing yellow gas there is now a dark line, and on 
either side of it the spectrum stretches in all its beauty, 
violet at one end, red at the other. The dark line lies 
in that part of the spectrum which is of a yellow color. 
If the spirit lamp be now removed, the dark line in the 
yellow of the spectrum disappears, and the spectrum is, 
as at first, a variously colored ribbon, in which there are 
no dark lines. What caused the dark line, which has 
now vanished ? The bright white light is composed of 
all sorts of colors, among which is yellow. When this 



Further 



164 A Study of the Sky. 

light shone through the hot yellow gas in the spirit- 
flame, the gas absorbed some of it, so that there was a 
dark place in the yellow of the spectrum. 
Three prin- By numerous experiments the following principles 

have been established : 

Principle I. An incandescent solid or liquid, or a 
glowing gas which is made dense by the application of 
pressure, produces a spectrum, which is a ribbon of light 
of various colors, as previously described. This is a 
continuous spectrum. 

Principle II. A heated gas, which is composed of 
only one chemical element, gives a spectrum consisting 
of one or more bright lines. This is a bright-line 
spectrum. 

Principle III. A white light shining through a gas 
produces a spectrum which would be continuous if it 
were not crossed by dark lines. The dark lines cor- 
respond in position to the bright lines in the spectrum 
of the gas. This is a reversed spectrum. 

How does an astronomer apply these principles ? 

The principles . , . , 

applied. He takes on the eye-end of his telescope, and attaches 

the spectroscope instead. The instrument is directed 
at a nebula ; the light from the nebula enters the spec- 
troscope slit, passes through the prism, and produces a 
spectrum of bright lines. The nebula is therefore a 
glowing gas. By comparing the spectrum of the nebula 
with the spectrum of hydrogen, for instance, it is proven 
that hydrogen is present in the nebula. 

The spectrum of the sun is a reversed spectrum 
crowded with thousands of dark lines. White light 
coming from the sun's interior passes through the 
heated gases in his atmosphere, and suffers absorption, 
according to Principle III. A spectroscope can be so 
constructed that the spectrum of the vapor of sodium 



The Astronomer s Workshop. 



165 



will be shown in the field of view, just below the solar 
spectrum. The prominent lines in the sodium spectrum 
are just below certain dark ones in the solar spectrum. 
Sodium is therefore in the sun. 

What would the observer conclude about the nebula 
in Andromeda if its spectrum were continuous ? 

Powerful spectroscopes are provided with more than 
one prism, and are too complicated to be explained 
easily. 

For certain classes of work prisms are rejected, their 
place being taken by a diffraction grating, which is a 




Fig. 89.— A Spectroscope. 

metallic mirror on the face of which thousands of fine 
lines have been ruled. Sometimes 40,000 lines are 
ruled side by side in a space an inch wide. White light 
is dispersed into its different colors by being reflected 
from the surface of the grating. 

There are many other astronomical tools, descriptions 
of which are forbidden by the limitations of this book. 
Mention must however be made of the photographer's 
camera, which is so common a piece of apparatus that a 
description of it is unnecessary. Many special photo- 



A grating. 



Photograph 



1 66 A Study of the Sky. 

graphic telescopes have been built, which have revealed 
objects too faint to be seen with the most powerful 
visual telescopes. To the results of photographic work 
in various astronomical lines, reference will be made 
from time to time. Very many departments of observa- 
Superiorre- tional astronomy have been invaded by the sensitive 
plate, which, despite its imperfections and limitations, is 
now admitted to furnish results superior to those 
obtained without its aid. 



CHAPTER X. 

TIME. 

" Old Time, in whose bank we deposit our notes, 
Is a miser who always wants guineas for groats ; 
He keeps all his customers still in arrears 
By lending them minutes and charging them years." 

— Holmes. 

In this busy age, when more progress is made in a 
minute than was formerly made in an hour, and the Importanceof 
exacting demands upon men in all walks of life make accurate time, 
them more chary of hours than their forefathers were of 
days, the importance of accurate time is realized as 
never before. The piercing whistle of the factory or 
machine shop wakes the echoes of the early morning 
at the exact moment when some steady clock reads 
seven, and hundreds of working people take their places 
promptly, to begin the day's toil. The railroad con- 
ductor, with pocket chronometer in his hand, stands 
beside the palatial through train, while the engineer 
holds the panting locomotive in check, till the signal is 
given to open the throttle and speed the waiting pas- 
sengers on their way. 

"Thirty seconds too late," says the depot clock, as 
the belated traveler hurries to the platform, only to Tard yp e °P le - 
find that the train has pulled out. " Our clock at home 
was five minutes slow," says the blushing schoolgirl, 
when called to account for her tardiness^ " The school 
clock must be a minute and a half too fast, ' ' says the 
boy who played marbles two minutes too long. The 

167 



i68 



A Study of the Sky. 



A wreck. 



Small fractions. 



Standard time. 



Time obser- 
vations. 



business man paces impatiently to and fro in his office, 
waiting for friends who were to come precisely at three. 
The electric car has just gone by, and the mistress of 
the house, arrayed for an afternoon's shopping, stands 
on her doorstep in a pet ; the kitchen clock was two 
minutes slow. The careful mariner, feeling his way 
along the coast, through a fog, feels a shock which 
shows that the good ship has struck a rock. The 
trusted chronometer has gone wrong, and the ship must 
go down in the seething floods. 

Scientists dispute about tenths of seconds, quibble 
over hundredths, and take still smaller fractions into 
account, while the world wonders how they contrive to 
measure intervals of time so minute. 

Though all the daily doings of the civilized world are 
governed to a large extent by the timekeepers which 
are to be found everywhere, few stop to inquire into the 
authoritative source of standard time, and the methods of 
its dissemination. People generally have vague notions 
that astronomers observe the sun when it is on the 
meridian, regulate their clocks accordingly, and then 
telegraph the time about for the benefit of railroads and 
jewelers. 

Let us go to the bottom of this matter, by visiting 
an observatory and seeing just what the astronomer 
does ; we must not go at mid-day, for he does not use 
the sun to get time by. In the evening we may find 
him at work, and fortunate shall we be if he permits us 
to sit down in the room where he is observing, and 
silently watch his operations. In the center of the dimly 
lighted room is the meridian circle, which we have 
described in Chapter IX. The roof shutters have been 
opened, and we may see the stars trooping past on their 
way to the western horizon. On a table near the 



Time. 



169 



instrument stands a chronometer, ticking off each half 
second ; by its side lies a book, containing a list of stars. 
The book gives the right ascension and declination of 
each star. The astronomer glances at his chronometer 
and sees that its reading is about 8 hr - 53 min - In the list 
he finds a star whose right ascension is 8 hr - 56 min - 
4.93 sec - The star therefore will cross his meridian about 
ghr. 56mm. ? anc f w iH come into the field of view of his 
instrument a few seconds before that time. 

Looking at the declination he mentally figures out the 
reading of the silver circle, when the telescope has the set. 
proper slant to the horizon. In a minute he has turned 
the telescope on its horizontal axis till the circle has the 
proper reading, and has applied his eye at the eyepiece. 
Faint stars come drifting through the field of view, 
shying past the golden spider-webs, as if they wished to 
escape from the astronomer's gaze as quickly as pos- 
sible ; but he pays no attention to them. 

In a short time the expected bright star appears on 
the edge of the field of view, glowing like a little sun. 
The observer glances quickly at the chronometer, and 
begins counting the readings of the second-hand ; 
"four, half, five, half, six, half," he says to himself, as 
he resumes his place at the eyepiece. The star moves 
onward ; it has leaped across the first spider-web, and 
the astronomer hurriedly writes in his note-book the 
figures 13. 1. 

He has estimated that the star crossed the first spider- 
web one tenth of a second after the chronometer ticked 
the thirteenth second of some minute. Hurriedly glanc- 
ing at the chronometer's face he again counts, and after 
a few seconds he makes another record, perchance 24.7. 
Thus he continues till the star has crossed the last 
spider-web ; having gotten the seconds and fractions of 



The star comes. 



Accurate esti- 
mates. 



170 



A Study of the Sky. 



The chronom- 
eter's error. 



Personal 
equation. 



a second as correctly as he can, he writes down the 
minute and the hour more leisurely. The record stands 
as follows : 

13.1 s -- 

24.7 

33-6 

42.4 

8 hr. 55 min. ^ r 

The average of these five times, obtained by dividing 
their sum by 5, is 8 hr - 55 min - 33-58 sec - That is the 
time, as nearly as the astronomer could estimate it, 
which the chronometer read when the star crossed his 
meridian. The book on the table states that the star 
really crossed the meridian at 8 hr - 56 min - 4.93 sec - 

The chronometer must therefore be in error ; by sub- 
tracting the chronometer time from the time given in 
the book, we get the remainder 3i.35 sec - Shall we not 
say that the chronometer is 3i.35 sec - slow? If the 
observer could estimate the time when the star crossed 
each spider-web accurately, and the instrument were 
perfectly adjusted in the meridian, one star would be 
sufficient. But the instrument has many errors, which 
must be taken into the reckoning, and the observer can- 
not do anything as accurately as he wishes. He there- 
fore observes several stars, and applies the refinements 
of mathematical analysis to the problem in order to 
determine the errors of the instrument, and make 
allowance for them. From the observation of each star 
he obtains a value of the error of the chronometer ; 
these he combines, taking their average as the final 
result. 

When the utmost obtainable accuracy is desired, the 
1 ' personal equation ' ' of the observer must be taken into 
account. It takes time for men to think ; the more 



Time. 171 

complicated the operation, the greater the time. In 
the case of eye and ear observations, such as have 
just been described, one impression reaches the brain 
through the eye, when the star crosses the wire. 
Another impression comes from the chronometer, and 
is transmitted by way of the ear. The brain is occupied 
with the process of counting, but when the two impres- 
sions arrive, it compares them, pronounces judgment, 
and directs the hand to make a certain record. If a 
man is especially trained he can do all this without 
losing his count of the chronometer-beats. He can 
even observe the times of transit across two or three 
wires without removing his eye from the eyepiece, or 
stopping to write anything down. 

In the case of chronographic observations, which chronographic 
have been described in Chapter IX., and which are now observations, 
generally used, the brain has much less to do. As 
before it receives an impression by way of the nerves of 
sight, and sends a mandate to the finger to touch the 
telegraph key. The mandate is obeyed, and the time 
is recorded almost instantaneously on the chronograph 
sheet. The personal equation for eye and ear observa- 
tions is usually greater than for chronographic work, 
because of the greater complexity of the process. 

A machine has been invented for determining the 
personal equation of a time observer. The observer 

. Personal 

looks through a little tube, resembling the eyepiece of a equation 

. . . ... machine. 

telescope, and sees an artificial star, which is driven by 
clockwork across a system of wires. The machine 
automatically records the time when the star crosses 
each wire ; the astronomer presses his telegraph key, 
as usual, and thus records the time when he thinks that 
the star crosses each wire. 

Such tests have demonstrated that the averaee 



172 



A Study of the Sky. 



Probable error. 



Error and rate. 



observer is between one and two tenths of a second 
behind time. Sometimes he has a habit of touching the 
key a few hundredths of a second before the star reaches 
the wire ; he probably estimates the rate at which the 
star is moving, and starts his mental machinery ahead of 
time, endeavoring to get the nervous impulse down 
to his finger at the time when the star arrives at the 
wire. In the case of eye and ear observations a discrep- 
ancy of over a second was once found between two 
noted astronomers ; the cause of so large a difference 
can only be guessed at. Apart from personal equation, 
the probable error of a time determination derived from 
a dozen stars is two or three hundredths of a second. 

Time, like money, is easier to get than to keep. 
After the error of a clock has been found, its rate must 
be sought. If on January 8, at 7 p. m. , a clock is 
io.93 sec - fast, and on January 11, at 7 p. m., another 
series of observations makes its error io.42 sec - fast, it 
has lost o.5i sec - in three days and is therefore losing 
o. i7 sec - a day. This rate is used in predicting the error 
for a few days ahead. If one wishes to know the error 
on January 13 at 7 p. m., he computes that the loss in 
two days is 2x0. i7 sec -, which equals o. 34 sec - ; since the 
clock was io.42 sec -fast on January 11, and has since lost 
o.34 sec -, it must be only io.o8 sec - fast. But the rate can 
be relied upon for only a few days ; the clock may be as 
fine as the maker can produce ; it may be enclosed in 
an air-tight case, so that variations in the pressure and 
humidity of the air have no appreciable effect upon it ; 
it may be put upon as solid a base as can be found, and 
in a room kept at as constant a temperature as possible ; 
it may be wound by an electric motor, so that the case 
need not be opened — yet its performance will not satisfy 
the astronomer. Week after week its rate will change 



Time. 173 

by small amounts, from obscure causes, which the 
astronomer cannot even foresee. Over and over again 
must observations be made, and calculations be carried 
through, that the time may be well kept. 

No endeavor is made to keep a standard clock right, 
for the constant changes which would be necessary 
would introduce intolerable disturbances into the clock's 
performance. It is therefore permitted to go on month 
after month, without alteration, its errors and rates 
being determined from time to time by observations of 
the stars. 

We have seen how an astronomer gets time, and how Time dissemi . 
he endeavors to keep it. We shall now see how he nated> 
disseminates it for the benefit of the country at large. 

Here electricity comes into play ; as a telegraph 
operator by touching his key can make any sounder on 
the line tick, so a clock may be arranged to accomplish 
the same end. While the second-hand is flying from 
one second to the next one, a tooth of a wheel mounted 
on the same arbor as the second-hand strikes a miniature 
telegraph key, and the signal is sent. One of the clocks 
at the United States Naval Observatory at Washington 
sends a signal over the Western Union wires to distant 
cities day after day, and thousands of telegraphic instru- 
ments tick as the signal passes. 

The sending of the signal is but a small part of the 
work of disseminating the time. In some cities a time 
ball is hoisted to the top of a pole a few minutes before 
noon, and released at noon by an electrical impulse. In 
others the fire bells are rung at the same hour. The 
Western Union Telegraph Company controls a system 
of clocks, which are set automatically once a day, when 
a signal is sent to them. Thus a business man may 
have reasonably correct time in his office, if he is willing 



Special devices. 



i?4 



A Study of the Sky. 



Standard 
meridians. 



Improvements 
in the plan. 



to pay the small rental charged by the company.^ The 
system conduces to the accurate running of trains, for 
every important railway station contains a telegraph office. 

The system of standard meridians, which has been 
adopted by the railroads and by the most important 
municipalities, is a great convenience. The trains in 
the eastern portion of the United States are governed 
by Eastern Standard time, which is five hours later than 
Greenwich time, and is not far from local time at Phila- 
delphia. Central Standard time is six hours later than 
Greenwich time, and is used in the Mississippi Valley 
and adjacent states. It is nearly the same as local time 
at St. Louis. Mountain time differs from Greenwich 
time by seven hours, and dominates the semi-arid region 
formerly known as the Great American Desert. The 
seven-hour meridian passes through Denver. Pacific 
time, one hour slower still, is the standard for the 
Pacific coast. The eight-hour meridian passes centrally 
through California. 

Two further improvements upon this plan may yet be 
made. There should be no insurmountable difficulty in 
having the time the same throughout any given state. 
The fact that the meridian by which Central time is 
governed runs near the Mississippi River much facili- 
tates the grouping of the states in such a way that the 
time which should be adopted in each one is easily 
remembered, f 



* The clocks furnished are of a fair grade, and are expected to vary only a 
few seconds a day. They are set just right by the signal, and if they do not 
get out more than twenty seconds during the ensuing twenty-four hours, the 
next signal sets them right again. A rate of twenty seconds a day is rare. 
The system has therefore a high efficiency. 

f Central Standard time should be in force in all the states which border on 
the Mississippi, and the three great lakes, Superior, Michigan, and Huron, 
together with Alabama. These states are Michigan, Indiana, Kentucky, 
Tennessee, Alabama, Wisconsin, Illinois, Mississippi, Missouri, Arkansas, and 
Louisiana. 

Eastern time should be the standard in all states east of the preceding ones. 
These are Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, 



Time. 



175 



A twenty-four- 
hour day. 



Astronomical 
and civil date. 



A further desirable change, which would be more 
difficult of accomplishment, because of the conservatism 
of even so progressive a people as Americans, is count- 
ing the hours continuously through the day from one to 
twenty-four. The designations, a. m. and p. m. , would 
then be unnecessary. This system has already been 
tried upon the Canadian Pacific Railway, and is in force 
in Italy. Its advantages are simplicity and accuracy. 
Astronomers already have a twenty-four-hour day, 
which begins at noon. 

The business man prefers to have the date change at 
midnight, when he is usually asleep. The astronomer 
finds it inconvenient to change the date at midnight, 
when he is frequently engaged in observation. The 
astronomical day begins twelve hours later than the civil 
day ; January 5, 10 a. m., is January 4, 22 hours, by 
astronomical reckoning. March 16, 8 p. m., is March 
16, 8 hours, astronomically reckoned. Astronomers 
have of late years discussed the advisability of making 
their day begin at the same time as the civil day, viz. , 
at midnight, but they have not yet made the change. 

Europe is much in advance of America in the matter 
of time distribution. The city of Paris is supplied with Europe 
a system of electrical clocks, and also w r ith a system of 
pneumatic clocks, which, as their name indicates, are 
driven by compressed air. The standard clocks are so 
numerous that any one may learn the time accurately, 
with little trouble. Many small municipalities have 
extensive systems of electrical dials. 



Time in 



Connecticut, New Jersey, Maryland, the Virginias, the Carolinas, Georgia, 
Florida, New York, Pennsylvania, and Ohio. 

Mountain time should prevail in the first double row of states and territories 
west of the states which have Central time. These are the Dakotas, Nebraska, 
Kansas, Indian Territory, Oklahoma, Texas, Montana, Wyoming, Colorado, 
and New Mexico. 

Pacific time should be adopted by all the remaining states. These are 
Idaho, Utah, Arizona, Washington, Oregon, Nevada, and California. 



176 



A Study of the Sky. 



Time distri- 
bution in 
Great Britain. 



Watches. 



The Breguet 
spring. 



Compensation 
for temperature. 



One of the most elaborate systems of time distribution 
is to be found in Great Britain. The Royal Observatory 
at Greenwich is the source of accurate time, which is 
telegraphed over the United Kingdom. A time ball is 
dropped at Greenwich, for the use of ships in the 
Thames. Another at Deal serves the shipping in the 
Downs. The great clock at Westminster Palace is 
regulated in accordance with the telegraphic signals. 
Through the post-office department are sent signals 
which are utilized in various ways, such as the regulation 
of clocks, the striking of bells, and the firing of guns. 

However elaborately accurate time may be distributed 
in a given city, business men rely upon their watches, 
which are compared from time to time with some time- 
piece supposed to be a standard. The price of a watch 
movement is, in general, a good indication of its quality ; 
so excellent are the products of American makers, that 
one need not buy a foreign watch in order to get a good 
timepiece. In purchasing a watch of moderate price 
one may get an approximate idea of its excellence by 
paying attention to certain details. The more jewels 
the better. The hair-spring should be composed of a 
number of closely packed coils ; if the end of the outer- 
most coil comes in toward the center, overlying the 
other coils, the hair-spring is a " Breguet," which is the 
best form. The rim of the balance wheel should be 
made of two metals, the outer one brass and the inner 
one steel. This combination is of no use unless the rim 
has been cut through at two opposite points. 

A fair compensation for changes of temperature is 
obtained by using this form of balance. All modern 
American movements, unless very cheap, have compen- 
sation balances. When hot weather comes the hair- 
spring loses strength, and the balance must become 



Time. 



177 



smaller in diameter, if it is to be driven as rapidly as 
before. The brass in the rim expands in the heat more 
than the steel does ; thus each half of the rim is bent 
inward, and the diameter of the balance grows less. 
When the watch is exposed to cold the hair-spring- 
acquires more vigor, and the watch tends to gain ; but 
the outer brass portion of the rim contracts more than 
the inner steel portion, and each half of the ring bends 
outward, increasing the inertia of the wheel, and thus 
preventing the gain which would otherwise ensue. 



a watch one should compare it The rate of 

a watch. 



To test the running of 
with a standard clock 
every day, or even 
more often, until a 
satisfactory knowl- 
edge of its perform- 
ance has been ob- 
tained. A watch 
which is set right to- 
day and found nearly 
correct a month after- 
ward may meanwhile 
have wandered off 

tWO or three minutes, Fig. 90.— A Watch Balance. 

and come back again. Sometimes a watch exhibits a 
large daily variation, gaining a considerable fraction of a 
minute during the first few hours after it is wound, and 
losing it during the remainder of the day. 

It is needless to say that a watch must be treated well, 
if it is expected to do good work. It must not be 
handled carelessly, nor be permitted to run down ; if it 
runs down, it rarely starts again with the same rate that 
it had previously. Unless a watch is expensive, and 
''adjusted for heat, cold, and position," it is likely to 




Good treat- 
ment. 



i 7 8 



A Study of the Sky. 



Ladies cul- 
pable. 



The regulator. 



Miscellaneous 
facts. 



exhibit considerable variations of rate, if it is not kept in 
nearly the same position at night as in the daytime. It 
is not a good plan to put a watch under one's pillow. 

Ladies are especially culpable in the matter of hand- 
ling their watches. They do not wind them regularly, 
and they let them lie around in bureau drawers or 
handkerchief boxes, or other places where they are con- 
sidered safe for the time being. For these reasons 
ladies' watches rarely keep good time. 

A young man is likely to move the regulator too 
often. If his watch suddenly begins to gain a few 
seconds a day, the regulator is moved backward at 
once. The less one alters the regulator the better, for 
a watch, like a human being, is subject to spells of 
irregularity, from which it recovers if left to itself. 

If the minute-hand is once set exactly over a minute 
mark, when the second-hand is at 60, and the two 
hands do not keep together, either the face is poorly 
engraved, or the pinion on which the minute-hand turns 
is not in the center of the face. If either of these hands 
slipped, which is rarely the case, the same effect would 
be produced. 

Occasionally a watch gains a minute or so in an hour; 
this indicates that the hair-spring is caught, so that it 
does not vibrate freely ; a jeweler will loosen it in a 
moment. A watch may stop because it has been 
wound too tightly ; a little shaking for a few minutes in 
such a way as to make the balance wheel vibrate will 
relieve the difficulty. 

In general, the possessor of a watch does his full duty 
by it if he winds it regularly, handles it carefully, keeps 
it in the same position as much as possible, and has it 
cleaned once in two years. 



CHAPTER XL 



THE SUN. 



" See the sun ! 
God's crest upon His azure shield the heavens." 

— Bailey. 

Of all the heavenly bodies the sun is of the greatest 
importance to man. Without its steady gravitational its importance, 
pull on the earth our planet would fly away to unknown 
regions of space, and the chill of death would settle 
down upon it. The oceans would stiffen into glass : 
the rivers would halt in their courses. All the higher 
forms of vegetable life would wither and die, and 
humanity, having struggled in vain against inevitable 
fate, would perish of hunger and cold. For the human 
race is dependent upon the energy which the sun 
radiates so lavishly. 

The sun stimulates the growing plant to disengage 
carbon from the embrace of oxygen, feeding on the ^Slf" a " d 
carbon and leaving the oxygen, which is necessary for 
the life of men and animals. Its heat evaporates the 
waters of the oceans, which rise, form clouds, and 
descend again as rain or dew, quenching the longings 
of the parched earth, nourishing vegetation, coursing in 
majestic rivers to the sea, refreshing the bodies of men 
and animals, and giving delight to all intelligent spirits. 

The energies of the sunbeams were stored ages ago in 
primeval forests : the forests were overwhelmed by the 
mighty deep and buried in a sepulcher of stone. To- 
day men dig up the mummified sunbeams and burn 



Mummified 
sunbeams. 



i So A Study of the Sky. 

them in their furnaces and fireplaces. The genial light 
of the grate fire is due to those ancient sunbeams which 
are now released from their prison house. The flying 
locomotive, beneath whose impetuous rush the earth 
trembles, gets its speed from the sunbeams. The white- 
hot glow of a Bessemer converter comes primarily from 
the sun. The water which flows into our houses has 
been purified by the sun's rays, and has been forced 
through the pipes by great engines which derive their 
power from solar energy stored in coal. The electric 
car is driven by a current generated by a dynamo, and 
the dynamo in turn by a steam engine which is fed 
with the sunbeams of bygone ages. The electric light, 
which turns night into day, is stray sunshine. Nearly 
all the heavy work of the civilized world is done by the 
sun. 

Bread, which is the staff of life, comes from wheat 
The staff of which has been stimulated in its growth by the sun- 
beams, and moistened by water lifted by the sun. If 
the mill which reduced the wheat to flour was driven by 
the wind, we find the source of the wind in heat pro- 
duced by the sun's rays. If the mill was driven by 
water power or by steam, we still say that the sun sup- 
plied the power which turns the millstones. Even the 
final process of baking the bread is an application of 
heat originally derived from the sun. A man's muscles 
obtain their strength from the food which he has eaten : 
in the food has been stored the energy of the sun. 

In fine, we owe to the sun the sustenance of our 
bodies, the maintenance of our physical energies, the 
comforts which we enjoy, the cooling breeze, the gentle 
shower, and the manifold beauties of nature. We pro- 
ceed therefore to a short study of this wonder-working 
body, and shall endeavor to gain some notions about its 



The Sun. 



distance, its size, its motion, its changes of appearance, 
its make-up, its energies, and its future. 

The distance of the sun from the earth is nearly T he sun's 
93,000,000 miles. If a straight road were built from 
the earth to the sun, and the earth, rotating at its 
present speed, were to start along this highway, like a 
rolling wheel, more than ten years would elapse before 
it would reach the sun. For in one day it would travel 
a distance equal to its own girth, which we will call 
25,000 miles. In forty days 1,000,000 miles would 
have been left behind ; over 3,700 days would therefore 
be consumed in the entire journey. An express train, 
traveling fifty miles an hour day and night, without 
intermission, would require over two centuries to trav- 
erse the same distance. 

There are many ways of finding the distance of the Howthedis 
sun, most of which involve complicated mathematical tance is found. 
operations. But one of them is easily understood. By 
a series of beautiful and accurate experiments physicists 
have measured the velocity of light, which they place at 
186,330 miles a second. Astronomers have found that 
light takes 499 seconds to come from the sun. There- 
fore the distance of the sun is obtained by multiplying 
these two numbers together. This is the mean distance 
of the earth from the sun. Since the orbit of the earth 
is not a perfect circle, but an ellipse, its distance from 
the sun varies. It is nearest to the sun at the beginning 
of the year; six months later, on July 1, it is almost 
3,000,000 miles further away. 

When the distance of the sun is known its diameter 
is easily computed. It is 866,500 miles; this is nearly The diameter, 
no times the earth's diameter. The sun is therefore 
over 1,300,000 times as large as the earth. If the earth 
were magnified until it became as laroe as the sun, and 



182 



A Study of the Sky. 



Use of a 
telescope. 



Spots. 



Rotation. 



the sizes of its inhabitants were increased in like ratio, a 
man originally 5 feet 1 1 inches in height would become 
650 feet tall. If the force of gravity were no stronger 
than at present, his original weight would be multiplied 
by 1,331,000. But, according to the principles of 
mechanics, the earth's attraction for a body upon its 
surface would be no times as great as before; hence 
our unfortunate human being would weigh over 10,000,- 
000 tons, if his former weight was only 140 pounds. 

When the sun is viewed with a telescope especial pre- 
cautions are taken to diminish the intense light, so that 
the eye of the observer may not be ruined. A very 
dark glass held in front of the eye will furnish the needed 
protection, but it may become too hot and break. Special 
forms of eyepieces have been devised, which allow most 
of the light and heat to escape, reflecting only a small 
part of it to the observer's eye. 

A cursory examination with even a small telescope 
reveals the existence of small black spots upon the solar 
surface. Each spot is surrounded by a lighter border, 
which appears to be composed of a large number of fila- 
ments, like the fringe around a table-mat. The dark 
portion of the spot is called its umbra ; the surrounding 
border is the penumbra. 

If an observer makes a drawing showing the posi- 
tions of the spots on the solar disc, and looks at them 
again in a day or two, he sees that they have moved. A 
watch of a few days will convince him that they are 
being carried around at a pretty regular rate, and that 
the sun, like the earth, turns on an axis, making a com- 
plete rotation in three weeks and a half. 

Spots near the solar equator revolve in twenty-five 
days and a fraction ; those which are nearly midway 
between the poles and the equator consume twenty- 



The Sim. 183 



seven days in making one revolution. Spots are never 

seen more than half way from the equator to the poles, J^istri bution of 

and are much less numerous near the equator than a few 

degrees away from it. This strange distribution of the 

spots, together with the curious irregularity in their 



/ 

/'■■ 


* Mfm 




*4 


V 




**> • 




y 




f-"*** 


4 






Fig. 91.— Sun-spots. 

times of revolution, constitutes the first of a number of 
unexplained mysteries concerning the solar surface. 

When a large spot is on the edge of the sun's disc, 
one may see that it makes a slight notch in the sun's depression. 
limb (as the edge of the disc is called). Therefore 
the spot must be a depression below the grayish-white 
surface of the sun. The shape of the spot is like that of 
a dinner plate, the bottom of the plate corresponding to 



1 84 



A Study of the Sky. 



Sizes of spots. 



the umbra, and the gently sloping rim to the penumbra. 

Spots vary in size from the merest black points, just 

visible with high telescopic power, to immense objects, 





9&»L 



2+ 






it** 

v\*# 4?«*' 
\\ 






Fig. 92.— Changes in a Solar Spot. 
covering thousands of millions of square miles. One of 
A rou rgeSpot " ^ e l ar g eSL spot-groups on record had a diameter of 
150,000 miles. The central spot of a large group, 



The Sun. 185 



which appeared in February, 1892, measured 100,000 
miles by 50,000 miles. Such enormous objects are 
easily visible to the naked eye if it be protected by a 
dark glass. 

Sun-spots change their appearance from day to day, 
and frequently from hour to hour. At times a white Their changes, 
bridge may span the black gulf of the umbra ; at other 
times the umbra may be almost entirely hidden by a 
grayish veil similar in appearance to terrestrial clouds. 
The filaments of tire penumbra, which are usually nearly 
straight, may become violently curved and distorted. 
Occasionally the appearance of the filaments indicates 
that the spot has a rotary motion, like that of a terres- 
trial whirlwind. A spot frequently breaks up into a mul- 
titude of smaller ones. A group of small ones may 
coalesce into a single large one. 

In July, 1892, a double sun-spot, consisting of two 
umbrae, separated by a bright bridge, and surrounded 
by a common penumbra, experienced a very rapid 
change of appearance. A bright jet of white matter 
shot out over one of the umbrae, and when photographed 
presented the appearance of a gigantic fish-hook, carry- 
ing at its extremity a huge ball of light. This was 
but the precursor of a terrific commotion, for, after half 
an hour, it was found that a multitude of outbursts had 
taken place, so that the spot was completely hidden. 
This solar storm, which extended over billions of square 
miles, was not in the sun-spot, but high above it. Some- 
times, when our atmospheric conditions are peculiar, a 
clear sky is converted into a cloudy one in the course of 
a few minutes, and the clouds pass away again in a few 
hours. The solar disturbance behaved in a similar 
fashion ; in two hours after the disappearance of the 
spot it was again in view, unscathed by the tempest. 



A solar tempest. 



i86 



A Study of the Sky. 



Duration and 
death. 



Periodicity. 



The photo- 
sphere. 



A sun-spot usually lasts a few weeks ; one is on 
record which was observed for eighteen months. The 
death of a sun-spot is a short process. The surround- 
ing material rushes pell-mell into the cavity, and all is 
over. 

One of the most remarkable facts about sun-spots is 
their periodicity. At times the sun is almost free from 
them for a number of successive weeks. At other times 
they are to be counted by tens and even run up into the 
hundreds. When the first quarter of the nineteenth 
century had been rounded out, a persevering German, 
Schwabe by name, who was a magistrate in the town of 
Dessau, being possessed of a telescope and a large fund 
of patience, resolved that he would watch the sun day 
by day and count the number of spots. So it came to 
pass that the sun found Schwabe continually on the alert 
for over forty years. 

An examination of his record books, after he had 
been at work nearly twenty years, revealed something 
quite unexpected. He quaintly said that, like Saul, he 
went out to seek his father's asses, and found a king- 
dom. His discovery was that there was a certain 
regularity about the number of spots visible. If spots 
were decidedly scarce in a given year, the next year the 
number was larger, the next year larger still, and so on, 
until the fifth or sixth year, when the number was 
greatest ; during the ensuing year they were fewer, and 
after that their number diminished until it became a 
minimum again. Eleven years and a fraction elapse 
between one minimum and the next one. The period 
of eleven years is subject to irregular variations of a year 
or more. 

Considerable light is thrown on the nature of sun- 
spots by a knowledge of the medium in which they 



The Sun. 



187 



reside. It is called the photosphere, because it is the 
light-giving surface directly visible to us. It is analo- 
gous to the crust of the earth, but is far from being nJ t °so?& here 
solid. The heat of the sun is so intense that any known 
solid would be quickly melted and vaporized, if dropped 








Fig. 93.— A Portion of the Photosphere. 

into its fiery bosom. The photosphere is a sheet of 
luminous clouds, floating in an intensely heated gas, as 
terrestrial clouds float in our atmosphere. It is not of 
uniform brightness, but consists of a grayish back- 
ground, plentifully besprinkled with comparatively small 
masses of greater brightness. If great things may be 
compared with insignificant ones, the photosphere may 



A sheet of 
clouds. 



The solar 
interior. 



1 88 A Study of the Sky. 

be said to resemble a plate of rice-soup. The solar 
' ' rice-grains ' ' average 500 miles in width, and are 
themselves composed of smaller "granules," compacted 
together. 

Three quarters of the sun's light is derived from the 
rice-grains, which cover about one fifth of the entire 
surface. They are by some supposed to be the upper 
ends of ascending currents, rising from the intensely 
heated interior ; the dark spaces between the spots, 
according to this view, mark the terminations of streams 
of matter which have been cooled somewhat and are 
descending. The penumbrae of sun-spots contain long- 
drawn-out rice-grains. 

The interior of the sun is thought to be mainly 
gaseous, because of the intense heat which must prevail 
there. Near the center the gases may be changed to 
liquids because of the enormous pressure of the superin- 
cumbent fluids. A heat, the intensity of which no man 
has the temerity to estimate, strives to expand the gases 
imprisoned beneath the overlying photosphere. 

From time to time outbursts occur at weak places in 
the photosphere ; the pressure from below is temporarily 
relieved in the locality of the outbreak, and the photo- 
sphere in that region sinks a little, forming the shallow 
basin of a sun-spot. The uprushing gaseous matter, like 
a stream of water thrown by a fire engine, rises to a 
certain height, and falls back again upon the solar 
surface. 
Origin of a spot But w hy is the umbra of a spot so dark? Since the 
umbra is depressed below the general level, and is over- 
laid by a greater depth of cooler vapors than the 
adjacent regions, it looks darker than they. For the 
light from the umbra, coming up through the vapors, 
is partially absorbed ; the umbra therefore looks dark 



The Sim. 



in contrast with the surrounding portions of the photo- 
sphere. However, the darkest portion of a spot is Acalcium 
brighter than a calcium light. When the force of the u s ht - 
eruption has expended itself and hot gases are no longer 
thrown up to great heights, to be cooled and precip- 
itated upon the solar surface, the spot ceases to exist. 

Such, in brief outline, is the most reasonable theory 
concerning the nature of sun-spots. Many other 
theories have been put forth from time to time, but they 
all seem open to very serious, if not fatal, objections. 

No satisfactory explanation has yet been advanced for 
the periodicity of spots, or for their absence from the 
polar regions. The paucity of our knowledge concern- 
ing these solar storms is not astonishing, in view of our 
ignorance about the whirlwinds and cyclones which stir 
up limited portions of our own atmosphere. 

While the photosphere is depressed in the locality 
where a sun-spot lies, it is elevated in numerous other 
places. The elevations are called faculce, and are Facuice. 
specially numerous in the neighborhood of spots. The 
agitations to which the photosphere is subject seem to 
raise its outer surface in mountainous ridges and isolated 
crests like the waves of a choppy sea. These elevations 
of photospheric matter sometimes rise to a height of 
several hundred miles, and look much brighter than the 
surrounding regions, as there is less gas above their 
summits to absorb their light on its journey to our eyes. 
Recent photographs show that the fainter faculce extend 
in a network over the entire photosphere, as shown in 
Fig. 94. The sensitive plates bear mute witness to the 
photospheric tumults. 

When the moon causes a total eclipse of the sun by The chromo . 
coming between that luminary and the earth, it covers sphere - 
up the dazzling photosphere, and permits less brilliant 



i go 



A Study of the Sky. 



A scarlet 
envelope. 



gases in its vicinity to be seen. The photosphere is 
thus found to be covered by a scarlet envelope called 
the chromosphere (color sphere). Its depth is 5,000 




Fig. 94. — Facul^e. 

miles, and it, like the photosphere, is agitated by tremen- 
dous forces. 
Prominences. Rising from it are beautiful scarlet forms of various 

shapes, which have been named protuberances, or 
prominences. Some of them look like huge trees, with 
trunks thousands of miles in diameter, and tops spread- 
ing out to great distances. The top of such a promi- 
nence is often connected with the chromosphere by 



The Sun. 



191 



smaller trunks, so that the whole resembles a huge 
banyan tree. Some look like jets of fiery liquid, and Fieryjets. 
remind one of the streams of water thrown by fire 
engines. A few resemble huge billows of flame. Some- 
times cloud-like masses of chromospheric matter float 
above the chromosphere, having no apparent connection 
with it. One has been noticed which was 475,000 
miles above the solar surface. Thanks to the spectro- 
scope these beautiful objects may now be observed any 
clear day when the sun is shining in its full strength. 
The most interesting prominence ever seen was ob- 




Fig. 95.— Prominences. 



served in the fall of 1871 by Prof. Chas. A. Young. * 
One day at noon he was looking at one of these objects, 
which was a long, low, red cloud, connected by four or 
five stems with the chromosphere. It was remarkable 



A remarkable 
prominence. 



* Director of the observatory at Princeton, N. J. 



192 



A Study of the Sky 



A.n explosion. 



only for its size, being about 100,000 miles long and 
half as broad. At 12:30 p. m. he was called away, 
having noticed nothing special, except that below one 
end of the prominence a small bright lump had de- 
veloped on the solar surface. In twenty-five minutes 
he returned, but the prominence was gone. The small 
bright lump had apparently become a surging flame, 
rising to a height of 50,000 miles. The prominence 
had been blown into shreds by some tremendous ex- 
plosion, and the debris of its wreck was rising 400 




Two classes of 
prominences. 



Fig. 96. — A Quiescent Prominence. 

times as swiftly as a rifle bullet flies. In ten minutes it 
had reached a height of 200,000 miles. At 1:15 p. m. 
only a few shreds of the prominence were visible. 

Prominences are divided into two classes, the quiescent 
and the eruptive. The former are the cloud-like forms 
which have been already mentioned ; they are com- 
posed mainly of hydrogen and helium.* The latter are 
fiery fountains which sometimes rush forth with veloci- 

* When helium was named it was supposed to be found in the sun alone. 
But it was discovered along with argon, and has since been found in rare 
minerals. It also rises from particular springs in the Black Forest and else- 
where. 



The Sun. 193 



ties exceeding 300 miles a second. Since the velocity is 
never measured at the start, when it is greatest, before 
it has been diminished by the resistance of the gas 
through which it flies, and by the backward pull of the 
sun, which is nearly twenty-eight times as great as the 
pull at the earth's surface, its original value may be as 
great as 500 miles a second. Some of these eruptions 
hurl masses of heated gas so swiftly that the sun's 
attraction cannot hold them back, and they escape into 
space, are condensed into solid bodies, and fly away to 
regions unknown. 

The lightning-girt cyclone strikes terror to men's 
hearts, as it plows through a town, uprooting the stur- 
diest trees, and tearing in pieces structures of solid 
masonry. But how insignificant it is compared with a 
jet of glowing gas, which travels further in a second 
than the cyclone does in an hour, and which, if it should 
strike the continent of North America, would turn its 
surface into a glowing cinder in a minute. 

Such a storm, "coming down upon us from the north, 
would in thirty seconds after it had crossed the St. 
Lawrence be in the Gulf of Mexico, carrying with it 
the whole surface of the continent in a mass, not simply 
of ruin, but of glowing vapor, in which the vapors 
arising from the dissolution of the materials composing 
the cities of Boston, New York, and Chicago would be 
mixed in a single indistinguishable cloud. ' ' A terrestrial 
volcano may bury a city and cause the waters of an 
adjacent sea to boil. But many a solar eruption could 
fuse the earth into a misshapen lump. 

What is found beyond the chromosphere ? At the 
instant when a solar eclipse becomes total, and the moon 
hangs in mid-heaven, a black ball, fringed with the rosy 
prominences, it is surrounded by sheets of soft, pearly 



The fury of 
an eruptive 
prominence. 



The corona. 







111 

p ! 11 i Ill 

II I ■ ■ ■- 

WW^i ^ 

HP" 



II I II 

I lis I i I 1 lifi 



IMm < m 

wmlh : |! 

; til! ill ; * : ^^ : m 




The Sim. 195 



light, which form an aureole of surpassing beauty. 
The aureole has received the name ' ' corona, "as it is a 
crown of light upon the king of day. Its form varies. 
At times it is small in extent and roughly quadrangular 
in form. At other times it extends out in great stream- 
ers, as if the sun had wings. Streamers nearly 9,000,- 
000 miles in length were observed in 1878 from the sum- 
mit of Pike's Peak. Close to the sun the corona is 
bright, in marked contrast with the filmv streamers ; 
the inner corona is composed of fine filaments, closely 
packed together, which a small telescope shows beauti- 
fully. They closely resemble the finest of human hair. 

The corona is not to be considered as a solar atmos- Not a solar 
phere. Were that atmosphere. 

the case, it would 
decrease in density 
with a certain reg- 
ularity the further 
it extended from the 
sun ; it would also 
extend to about the 
same distance on all 
sides of the sun. 

When examined 
with the spectro- Fig. 98.— The Corona of January, 1889. 
scope it yields two different spectra. There is a faint 
continuous spectrum, which may come from sunlight re- 
flected from the materials composing the corona, or may 
be caused directly by white-hot solid or liquid particles 
scattered through the corona. The other spectrum is a 
bright-line spectrum coming from a glowing gas. The 
most prominent line in it is not identical with the spec- 
tral line of any substance found on the earth ; the name 
"coronium" has been proposed for the unknown sub- 




The spectra. 



196 



A Study of the Sky. 



Filaments. 



stance which causes it. Other lines reveal the presence 
of hydrogen and helium. 

Whence are these curious interlacing filaments of the 
inner corona, and the outstretched wings of the outer 




Fig. 99. — The Corona of April, 1893. 



Dark rifts. 



corona ? Why are dark rifts seen in certain places, as if 
the corona had been cleft by a gigantic cleaver from its 
outermost boundaries straight down to the solar surface? 
How are the materials composing the corona upheld 



The Sun. 197 



against the gravitational pull of the sun ? To these and 
other similar queries astronomers reply frankly that 
their knowledge is inadequate. 

That the coronal matter is excessively rarefied in its Rarefied 
higher regions is proven by the fact that several comets matter, 
have passed through it without any perceptible change 
in their motion. This rarefied matter may be upheld 
by an electrical repulsion originating in the sun. 

The fine filaments are due, perchance, to streams of Cause of th 
gas, which the sun is continually ejecting. Their curved filaments, 
forms and apparent interlacings are thought by Professor 
Schaeberle* to be due to the sun's rotation. 

Let us recapitulate what has been stated concerning 
the make-up of the sun: 

I. The interior of the sun is supposed to be mainly The sun's 
gaseous, the expansive power of the gases being held in make-up- 
check by the grip of gravitation. 

II. As the film of a soap-bubble confines the air 
within it, so the photosphere, which is the home of the 
sun-spots, strives to confine the imprisoned gases. It is 
composed of vapors which have been somewhat con- 
densed by their proximity to the cold of outer space. 

III. Certain light gases which do not condense so 
readily as those of which the photosphere is composed 
form a shallow layer covering the photosphere. The 
layer is of a scarlet hue, nourishes the prominences, and 
is called the chromosphere. 

IV. Beyond the chromosphere, and to a certain extent 
mingled with it, is the pearly corona, whose mysterious 
filaments and vast extension furnish food for much spec- 
ulation. 

Bright as full sunshine is, it may be compared with An experiment 
the light of a candle. Light screens are placed over with sunIi s ht - 

* J. M. Schaeberle, of the Lick Observatory. 



198 



A Study of the Sky. 



A standard 
candle. 



The moon and 
an arc light. 



The sun's heat. 



the windows of a room so that it is completely darkened. 
A small hole is made in one screen and a lens inserted 
in it. By manipulating a mirror outside, a horizontal 
beam of sunlight is thrown through the lens, which 
spreads out the beam of light, so that it illuminates a 
large circle on the opposite wall. If the diameter of the 
circle is 200 times the diameter of the lens, the area of 
the circle is 200 x 200, or 40,000 times as great as that 
of the lens. Therefore the beam of sunlight, when thus 
spread out, has only tofoo of its former intensity. A 
pencil is held in the enfeebled sunlight, close to the 
wall, so that its shadow is cast there. 

A standard candle is lighted and held in such a direc- 
tion from the pencil that the shadow which it casts on 
the wall is near the shadow cast by the sunlight. The 
candle is placed at such a distance from the pencil that 
the two shadows appear of equal intensity. In this 
manner the enfeebled sunlight is compared with the 
light of a standard candle. 

The intensity of the light of the full moon may be 
estimated in the same way ; it is found that sunlight is 
600,000 times as bright as the light of the full moon. 
An arc light approaches sunlight in intensity more 
nearly than any other artificial light. Yet if we view 
with a dark glass an arc light which is directly in line 
with the sun, it appears as a dark spot on the solar sur- 
face. It is about one third as intense as sunlight. 

The amount of heat which the sun sends to the earth 
is determined by allowing a beam of sunlight to shine 
upon a quantity of water, and measuring the rise of 
temperature thus caused. In this way it has been found 
that if the earth were entirely covered with a blanket of 
ice 165 feet thick, and the heat sent us by the sun were 
uniformly distributed over the ice, it would .be melted 



The Sun. 199 



in a year. An ice blanket of equal thickness, covering 
the sun, would be melted off in three minutes. If the 
solar heat was dependent upon the combustion of coal, 
a chunk of the best anthracite as big as the moon would 
have to be fed to the sun every forty-five minutes. 

The earth receives but a small fraction of the light 
and heat radiated by the sun. Imagine a hollow sphere portion of it. 
of crystal, the center of which is at the sun, the surface 
of the crystal shell being 93,000,000 miles from the sun. 
Let the earth be set, like an emerald, in the crystal An emerald in a 

J crystal sphere. 

shell. The amount of heat received by the shell in one 
second equals that emitted by the sun in the same time. 
Remove the emerald, leaving the hole in which it was 
set. Knowing the diameter of the earth, calculate the 
area cut out of the crystal shell by the hole ; it is about 
50,000,000 square miles. Also find the area of the 
surface of the crystal sphere. 

As the area of the hole is to the area of the sphere, so 
is the amount of heat received by the earth in one 
second to that radiated by the sun in the same time. 
Substituting the proper numbers in this proportion we 
find that the sun radiates 2,200,000,000 times as much 
light and heat as the earth receives. 

If a javelin of ice forty-five miles thick were hurled 
directly at the sun by some Titanic arm, with the 
velocity of light, and the entire outpour of solar heat 
were concentrated upon it, the threatening weapon 
would be melted as fast as it advanced. 

Not only do light and heat come from the sun, but 
electrical influences as well. In various parts of the influences 
world are magnetic observatories, where delicately sus- 
pended magnets swing gently to and fro in obedience to 
changes of magnetic force, and vibrate violently when 
thrilled by magnetic storms. In years when sun-spots 



A javelin of ice. 



Electrical 



200 



A Study of the Sky. 



A notable mag- 
netic storm. 



A chromo- 
spheric dis- 
turbance. 



are numerous, the magnetic needles are subject to 
numerous large oscillations, and the glimmering auroras 
coruscate in greatest splendor. When sun-spots are few 
the needles and auroras have a comparative rest. 

There are several instances where solar disturbances 
were observed at times of derangement of the earth's 
magnetic condition. 

On September i, 1859, a remarkable magnetic storm 
was in progress. Earth currents played havoc with 
telegraphic communication, and were at times sufficiently 
strong to work lines without the aid of batteries. At a 
station in Norway the telegraphic apparatus was set on 
fire. In this country the electric fluid established private 
lines in the nervous systems of operators without going 
through the formality of getting a franchise. The pen 
of a recording telegraph in Boston was followed by a 
flame. The shimmering auroras of the north made 
forays into the tropics. 

Late in the forenoon of that day an English astrono- 
mer, who had devoted many years to a study of sun- 
spots, was engaged in observing a large group ; he was 
startled by the appearance of two brilliant flashes, which 
dazzled his eye, though it was protected by a dark glass. 
In five minutes they had faded away, having apparently 
traveled a distance of 35,000 miles along the sun's disc. 

Professor Charles A. Young, when observing in the 
Rocky Mountains in 1872, saw, on the morning of 
August 3 at 8:45, 10:30, and 11:50, special disturbances 
of the chromosphere, caused by eruptive prominences of 
great brilliancy. At the same time the magnets in Eng- 
lish observatories twitched. Professor Young' s assistant, 
who was making magnetic observations, was obliged to 
desist, because the magnet swung clear off the scale. 

In the face of these and other similar coincidences. 



The Sun. 201 



one can scarcely doubt that solar disturbances bear some 
relation to magnetic storms. The nature of the connec- 
tion is not known, and some physicists doubt whether 
the electrical influences at work on the sun are of suffi- 
cient intensity to cause such violent terrestrial disturb- 
ances as are on record. 

Various attempts have been made to determine the 
effect of sun-spots upon the weather. Meteorological 
records have been diligently compared with those of sun- 
spots to see whether years when spots are plentiful are 
hotter or cooler than those when spots are few. The 
results obtained by different investigators are so conflict- 
ing that the question cannot be decided. An exhaustive 
study of the amount of rainfall in different years has 
shown that fluctuations probably exist resembling those 
of sun-spots. But much further research has yet to be 
made before conclusions which command confidence can 
be reached. 

If sun-spots had any marked effect upon meteorologi- 
cal conditions, the commerce of the world would be 
affected. Commercial crises have been investigated from 
this point of view, but nothing conclusive has been 
determined. As the years roll on, and both solar and 
meteorological phenomena are more diligently observed 
than in the past, some investigator may cause light to 
shine where darkness now reigns ; but enough has 
already been done to show that commotions on the sun's 
surface have very little, if any, effect upon meteorologi- 
cal conditions on the earth. 

The problem of the maintenance of the sun's heat is 



The weather. 



before us. During historic time the heat received from nance of the 
the earth has been practically constant in amount. In 
the main, plants grow to-day just where the same species 
flourished in the days of Pliny. Men needed fires to 



202 



A Study of the Sky, 



No observed 
changes. 



Combustion. 



The meteoric 
theory. 



warm their bodies in ancient times just as now, and were 
oppressed by the heat of midsummer as they are to-day. 
There is no trustworthy human record of any great 
migration of animals, which might be due to changes of 
temperature. The rocks, to be sure, tell of great 
changes in the remote past, epochs when high northern 
latitudes experienced tropical temperatures, and other 
epochs when the temperate zones were encased in ice. 
But no one knows whether these conditions were due to 
variations in the earth's distance from the sun or to 
changes in the intensity of the solar heat or to a combi- 
nation of both causes. Amazing as is the daily outpour 
of solar heat, there is no evidence from observation that 
it has changed in quantity or quality since human history 
began. 

The supply cannot be infinite ; how, then, is the 
radiation maintained? Not by combustion, for in 
that case the solar fires would have burned out ages ago. 
If the sun were a mass of the best hard coal, burning in 
oxygen, it would be consumed in sixty centuries. If 
combustion is excluded from the list of possible causes, 
what shall we say about the impact of bodies from with- 
out ? 

If a projectile from a rifled gun strikes the armor- 
plate of an ironclad, the shot is not only deformed but 
heated. If the earth should fall to the sun from its pres- 
ent distance, as much heat would be developed by the 
impact as the sun radiates in ninety-five years. The fall 
of giant Jupiter would cause an accession of heat equal 
to the amount now given off in over 30,000 years. Why 
may it not be that meteoric bodies fall upon it in suffi- 
cient numbers to keep up the supply of heat? We reply 
that if there were any such aggregation of meteors in 
the sun's vicinity it ought to have a marked effect upon 



The Sun. 203 



the motion of some comets which come near the sun, 
and would encounter it. Doubtless the sun receives 
some heat from such a source as this, but only a fraction 
of its heat can be thus accounted for. 

The theory generally accepted is called the contraction The contraction 
theory. When a body falls from any elevation to the theory - 
earth's surface, heat is produced when it strikes. If the 
same body be attached to a rope and made to turn a 
machine with badly oiled bearings, at least a portion of 
the energy of the descending body is converted into 
heat. In the first case energy is converted into heat 
suddenly, at the instant when the body strikes ; in the 
second case a portion of the energy of the descending 
weight is being gradually converted into heat. 

Without going more deeply into details we may say 
that if the sun be slowly contracting in size, so that the 
particles of matter which compose it are falling toward 
the center, heat is being produced by this contraction. 

If the sun's diameter diminishes five feet a week the 
total radiation of the sun is explained. Such a shrinkage 
is so slight that it would not be certainly detected by our 
present means of astronomical measurement in 10,000 
years. The contraction theory is considered the most 
reasonable which has yet been advanced. 

If all the heat which the sun gives out comes from its 

, .. , , , 1-1 , The sun's past 

contraction, and 11 the amount 01 heat radiated yearly is and future, 
practically constant from age to age, it is possible to 
reason backward to a time when the sun was inconceiv- 
ably vast, and to reason forward to a time when it will 
probably cease to give sufficient heat to maintain human 
life on the earth. Upon these hypotheses the sun would 
consume 18,000,000 years in radiating away the heat 
which would be developed by its contraction from a size 
inconceivably great to its present dimensions. Five mil- 



204 



A Study of the Sky. 



Contraction. 



Amusing 
speculations. 



lion years hence it will, upon this hypothesis, have only 
half its present diameter, and the matter composing it 
will be crowded into one eighth the space now occupied. 
The compression will probably turn most of it into a liquid 
or solid form. Further contraction being then very diffi- 
cult, the temperature of the sun will probably fall so 
rapidly that its function as a life-giver to the earth will 
cease before another 5,000,000 years have rolled away. 

Our reasoning has been based upon unverifiable hy- 
potheses and the conclusions may be far astray. They 
simply represent the best guessing that scientists can 
make with reference to the past and future of the sun. 
There is at any rate no reason for alarm at present. 

Mark Twain has well satirized scientific speculations 
which involve millions of years in the following passage : 

Now, if I wanted to be one of those ponderous scientific 
people, and " let on " to prove what had occurred in the remote 
past by what had occurred in a given time in the recent past, or 
what will occur in the far future by what has occurred in late 
years, what an opportunity is here ! Geology never had such 
a chance, nor such exact data to argue from ! Nor " develop- 
ment of species," either ! Glacial periods are great things, but 
they are vague, vague. Please observe : In the space of 176 
years the Lower Mississippi has shortened itself 242 miles. 
That is an average of a trifle over one and one third miles per 
year. Therefore, any calm person, who is not blind or idiotic, 
can see that in the old Oolitic Silurian period, just a million 
years ago next November, the Lower Mississippi was upwards 
of 1,300,000 miles long, and stuck out over the Gulf of Mexico 
like a fishing rod, and by the same token any person can see 
that 742 years from now the Lower Mississippi will be only a 
mile and three quarters long, and Cairo and New Orleans will 
have joined their streets together, and be plodding comfortably 
along under a single mayor and a mutual board of aldermen. 
There is something fascinating in science. One gets such 
wholesome results of conjecture out of such a trifling invest- 
ment of fact. 



Tides retard 
the earth 
rotation. 



CHAPTER XII. 

THE MOON AND ECLIPSES. 

" That orbed maiden, with white fire laden, 
Whom mortals call the moon, 
Glides glimmering o'er my fleece-like floor, 
By the midnight breezes strewn." 

— Shelley. 

Those who speculate about the origin of celestial 
bodies have a fine field of thought in connection with the earth's 
the moon. It is an undoubted fact that the moon 
raises tides in our oceans. The wash of the tides 
against continents and islands tends to retard the rota- 
tion of the earth by a trifling amount. If this retard- 
ation is not offset by other causes, as, for instance, a 
shrinking of the earth from its progressive cooling, the 
length of the day must be gradually increasing. The 
increase must be very slow, because it has not yet been 
brought to light by observation. The action of the 
moon upon the earth is accompanied by a reaction of 
the earth, which expresses itself in allowing the moon 
gradually to move farther and farther away. 

Reversing the process, we look back through geologic 
ages to a time when the earth whirled much faster than backward 
at present, and the moon was close to its surface, both 
bodies being hotter than now. How did these bodies 
come to be in such close companionship ? Does it not 
seem probable that they were originally one ? A grind- 
stone which rotates too rapidly bursts asunder. Is it 
not then entirely possible that when a mass of heated 



2o6 



A Study of the Sky. 



Looking 
forward. 



The moon's 
rotation. 



matter in a fluid state rotates rapidly, a piece of it may 
fly off? 

If we have hit upon a correct theory of the moon's 
origin, let us follow up the clue. The moon has dis- 
engaged itself from the earth, but is still held in check 
by the attraction of gravity, so that it is describing an 
orbit about the earth. Both bodies are in a fluid con- 
dition and rotating. They are so close together that 
the attraction of each raises large tides on the other. 
The tide on the earth checks the swiftness of its 
spinning. If the moon is rotating swiftly its tides put a 
brake upon it. If, on the other hand, it is rotating very 
slowly, the friction of the tides quickens its rotation. 

As previously mentioned, one result of this tidal 
action is that the two bodies separate. They grow 
cooler and more rigid ; the powerful tides raised upon 
the moon by the earth, keeping it continually egg- 
shaped, have had such an effect upon the original rota- 
tion that the moon has now solidified as a slightly 
elongated body, the longest axis of which points toward 
the earth. So it has come to pass that the moon keeps 
the same face turned toward the earth. 

If this be true, does it rotate at all? Certainly ; while 
it is making one revolution about the earth it also 
makes one complete rotation on its axis. This may be 
illustrated very simply. 

In the center of a circle one hundred yards in diame- 
ter a man is standing ; he watches a boy who runs at a 
uniform rate around the circle ; the boy keeps the left 
side of his head continually toward the man. At one 
instant the boy is facing the north ; in a few seconds he 
has run one fourth of the way around the circle, and 
faces westward ; in a few seconds more he faces south- 
ward, then eastward, and finally northward again, when 



The Moon and Eclipses. 



207 



he has completed the circuit. Since the boy has faced all a complete 
points of the compass successively he must have turned 
once around; but the man has seen only half of his head. 




Fig. 100. — Lunar Formations. 



If the boy had slackened the speed of his running at 

j.j.,,. 1 , e Why we see 

any time, out kept 011 turning at the same rate as before, more than half 
the man would have seen a little more of his face in 



208 



A Study of the Sky. 



Various 
reasons. 



Some data. 



The moon's 
phases. 



consequence. If the boy had quickened his pace at 
any time without changing the rate of his turning, the 
man would have gotten a view of a little more of the 
back of his head. 

The moon is not moving in a circle around the earth, 
but in an ellipse ; when it is nearest to us it moves 
more swiftly than when further away. But it rotates on 
its axis with a constant speed : thus we are enabled to 
see a little more than half of its entire surface. Further- 
more the moon does not stand upright ; that is, its axis 
is oblique to the plane of its orbit. Consequently we 
sometimes see beyond its north pole, and sometimes 
beyond the south pole. Also, as the earth turns, it 
carries the observer along and changes his point of 
view, so that he can see a trifle more of the moon than 
otherwise. Fifty-nine per cent of the moon's entire 
surface is thus presented to our view. The visible area 
is slightly more than double that of Europe. 

The moon's diameter is 2,163 miles, and its average 
distance from us is 238,840 miles. It is -h as large as 
the earth, but only fo as heavy. 

The moon's apparent changes of form result from its 
revolution around the earth, which is accomplished in 
27^ days. If it is to-day nearly on a line between the 
earth and the sun, it will not be in line again at the 
expiration of this period of time. For the earth has 
moved on meanwhile and altered the direction of the 
line. Thus it comes to pass that 29^ days elapse 
before the moon crosses the line again. 

Why then is not the sun hidden from view once every 
29^ days by the interposition of the moon's dark mass? 
The moon's orbit is tilted in such a way that the moon 
usually passes apparently above or below the sun, 
instead of in front of him. When the moon is nearly in 



The M0071 and Eclipses. 



209 



line between the sun and us, the sun lights up that half 
of it which is turned away from us, and the dark side is 
toward us. Besides this, the sun blinds our eyes, so 
that we can see nothing in his immediate neighborhood 
unless it be intensely bright. The moon is ' ' new. ' ' 

But in a couple of days our vision will be charmed by 
the sight of the young moon hanging low in the west in 
the evening twilight. Its position with reference to the 
sun has so changed that we can see a part of its bright 
hemisphere, as a graceful crescent. 

Most of the dark hemisphere of the moon is also 
visible. The earth plays the part of a mirror, and 
reflects back a portion of the sunlight which it receives. 
Some of this reflected sunlight lights up the dark side 
of the moon, so that we can see it. 

On the next night the moon is east of its former posi- 
tion, and sets later ; its crescent is larger. A week 
after new moon comes the phase of first quarter, when 
the moon is a bright semicircle off in the south at sun- 
set. On that evening and the three following its 
telescopic appearance is the most interesting. 

From night to night the illuminated disc grows larger, 
as the moon moves eastward, till it becomes a complete 
circle, and the moon is full. It then rises about sunset 
and sets about sunrise. 

During the next week the moon wanes and shrinks to 
a semicircle. One may then see it in the south at sun- 
rise, and in the southwest during the forenoon ; it is at 
the last quarter. The half moon changes to a diminish- 
ing crescent, and is lost in the sun's rays, as it becomes 
new again. 

When the moon is full, large dark brown areas are 
seen upon its face with the naked eye. According to 
Alexander von Humboldt the people of Asia Minor see 



Eaith shine. 



First quarter. 



Full moon. 



Last quarter. 



The face of the 
full moon. 



2IO 



A Study of the Sky. 



in these markings a resemblance to terrestrial seas and 
continents, and say that the moon exhibits a reflection 
of the earth as though it were a mirror. In the minds 
of many a human figure is outlined ; it has been super- 
judas iscariot. stitiously asserted that it is the figure of Judas Iscariot, 

whose sin has led 
to his being thus 
pilloried before 
the eyes of man- 
kind for all gen- 
erations. The 
casual onlooker 
perceives a hu- 
man face, the 
eyes, nose, and 
mouth being 
fairly conspicu- 
ous. Even chil- 
dren notice it. 

An opera-glass 
shows that the 
bright portions 
of the lunar sur- 
face are covered 
with rugged for- 
mations, while 
the dark portions 

Fig. i oi.— Lunar Plains, called Seas. are Smooth. 

When Galileo's telescope revealed these smooth regions 
The plains. they were supposed to be seas, which soon received 
such names as the Sea of Serenity, the Ocean of Tem- 
pests, and the Lake of Death. More powerful instru- 
ments show minute pits sunken all over the supposed 
seas ; they are therefore vast plains. 



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The Moon mid Eclipses. 211 

Great hopes were originally entertained that with 
increase of telescopic power would come evidences that JptEd^ower 
the moon was inhabited by intelligences, whose works 
would become manifest. It is doubtful whether any 
telescope that has already been constructed, or ever will 
be, can show the moon's surface better than it would be 
seen with the unassisted eye at a distance of 200 miles. 
A structure as large as the Liberal Arts Building at the 
World's Fair would be readily made out, if of a different 
color from the soil on which it was built. No details of 
the architecture could be distinguished, and one would 
never know whether it was a formation of nature or a 
structure erected by intelligent beings. Herschel once 
used a magnifying power of 7,000 diameters, which 
would theoretically bring the moon within thirty-five 
miles, but he could not see as well as if he had used a 
much lower amplification, because of ever-present at- 
mospheric disturbances. 

Despite this atmospheric handicap a vast amount of 

x . L Accuracy of 

lunar detail has been studied out, so that the topog- lunar maps, 
raphy of the side of our satellite which is turned 
toward us is much better known than that of vast areas 
of the earth's surface. 

For the geographical explorer has to press his way 
through deadly swamps, and across torrid deserts, 
scorched to the marrow by the sun, smitten by nameless 
fevers, tormented by insects, menaced by wild beasts, 
and ambushed by savages. The astronomer, on the 
other hand, sits in the seclusion of his observatory, in 
the quiet of a beautiful evening, making hi. ?measure- 
ments with inoffensive spider-webs, and recording them 
with a harmless pencil. 

The chief classes of lunar formations are craters, moun- 
tain ranges, isolated peaks, plains, rays, clefts, and rills. 



A summary. 



212 



A Study of the Sky 



The crater 
Copernicus. 



Other craters. 



A drop of water falling from the eaves of a house 
upon soft moist earth below makes a depression sur- 
rounded by a little wall of mud ; this resembles a lunar 
crater. 

One of the finest, situated not far from the center of 
the full moon, is named Copernicus (Fig. 102) ; it is fifty- 
six miles in diameter. To compare Vesuvius with it is 
to compare a pin-prick with a silver half dollar. In the 
center of the ring lies a rugged hill half a mile high, lifting 
its six heads up into the sunlight. The surrounding ring 
is beautifully terraced, as if there had been successive 
elevations and subsidences of lava in ages past. The 
summit of the ridge is a narrow ring, the top of which 
is over two miles above the floor of the crater. The 
surrounding region is thickly dotted with minute crater- 
lets. When the sun rises upon this magnificent crater 
the highest parts of the ring catch the sunbeams and 
outline the majestic circle. Within all is dark ; the sun 
rises higher and its light begins to creep down the inner 
wall of the further side of the crater. Yet all is dark 
within, and the central hill is invisible. Presently the 
six central peaks emerge one by one from the surround- 
ing darkness, and one can dimly descry the floor of the 
crater still enveloped in shadow, but rendered faintly 
visible by the light reflected from the illuminated portion 
of the inner wall. Hours wear away, and the interior is 
bathed in sunshine, except where short shadows hug a 
portion of the crater wall and nestle at the foot of the 
central hill. 

A few of the largest craters are over one hundred 
miles in diameter. In some cases the floors of craters 
are depressed below the general level of the surface ; in 
other cases the floors are elevated. It may be quite 
smooth, or it may be pitted with tiny craters and orna- 



The Moon and Eclipses. 



213 



mented with rugged hills. The walls may be precipi- 
tous in the extreme, or magnificently terraced and cut 







* 



Fig. 102. — Copernicus. 



up by yawning ravines. A man standing in the center 

of Schickard could not see the rampart surrounding Schickard. 

him, though it is over 10,000 feet high ; so rapidly does 



214 



A Study of the Sky. 



The 

Apennines. 



Pico. 



The plains. 



Rays. 



the moon's surface curve, because of its small diameter, 
that the top of the rampart would be below the man's 
horizon. One of the peaks within Clavius rises nearly 
five miles above the bottom of one of the craterlets at its 
foot. Sunlight never reaches the bottoms of some of 
the pits near the moon's poles. 

The finest mountain range is the Apennines (Fig. 
103). It is only 450 miles long, but the summits of its 
peaks rise to altitudes which rival those of the Andes. 
The loftiest peak lifts its head to the proud height of 
18,500 feet. On one side the entire range rises gradually 
from the plain ; on the other side it descends precipi- 
tously to the border of a " sea. ' ' The shadows cast by 
some of these peaks when the sun shines upon them are 
over 75 miles in length. The heights of mountains and 
of crater-rims are found by measuring the lengths of 
their shadows. 

Isolated mountains are rather rare. One of the finest 
is named Pico. Like the spire of some buried cathe- 
dral it rises abruptly from a level plane to a height of a 
mile and a half. A most imposing spectacle it would be 
to a man standing near its base. 

The great lunar plains, which have already been 
partially described, and which look quite smooth when 
viewed with a small telescope, lose their unruffled 
appearance when examined with a high magnifying 
power. The surface is covered with low ridges, and 
minute pits abound. 

Several of the larger craters are surrounded by fine 
systems of diverging rays, which are distinct at full 
moon. Tycho, a noble crater, the wall of which is 
17,000 feet high and fifty-four miles in diameter, is the 
center of the most conspicuous system of rays to be 
seen on the moon. It looks like the hub of a wagon 



The Moon and Eclipses. 



215 



wheel, from which the spokes radiate in all directions. 
The rays are whiter than the general surface and are 
often hundreds of miles in length. 

Clefts are cracks which appear in various regions. 
They are half a mile or so in width, and run in some in- 
stances hundreds of miles across plains and through 
craters, never halting at any obstacle. They are of 
unknown depth. Such a chasm upon the earth would 
strike terror to the heart of a traveler who found it 
lying across his path. 

Rills resemble the beds of ancient water courses ; 
they are, however, small, and not likely to catch the 
eye of the casual gazer. 

A body which was once hot and has cooled may well 
exhibit most of the peculiar formations which have just 
been described. Most of them have counterparts upon 
the earth. The neighborhood of the terrestrial crater 
Vesuvius is similar in appearance to many a portion of 
the lunar landscape. The craters cannot be closely 
likened to terrestrial volcanoes. The latter have small 
throats, and are surrounded by outpourings of lava. 
The former frequently embrace hundreds and even 
thousands of square miles within their walls, and do not 
appear to have deluged the surrounding country with 
the products of fiery outbreaks. The systems of rays 
can scarcely be due to overflows of lava. For in that 
case a ray would spread out, the further it got from the 
parent crater ; it would also be deflected when it en- 
countered another crater, and would be either heaped 
up, or would flow around it. But the rays are un- 
changed in width as they take their way across moun- 
tains and through craters. 

The general appearance of the lunar crust may be 
reproduced on a small scale by pouring the tap-cinder 



Clefts. 



Rills. 



Origin of 

the formations. 



Tap-cinder. 



ill 



~-> 






*» * . * 



. 



Fig. 103.— The Apennines. 
216 




The Moon and Eclipses. 217 

from a smelting furnace into a stout receptacle. At first 
a thin crust forms where the mass is exposed to the cool- 
ing action of the air. The crust is broken open in 
various spots by the action of the heated fluid. Some 
of the molten matter exudes through the holes ; a little 
ring is built up, or a cone-like structure. The contract- 
ing material within leaves the crust without adequate 
support and it cracks in weak places. Thus the work of 
solidification proceeds, and the final appearance of the 
crust bears a resemblance to the lunar surface. 

The question of changes in lunar topography during 
the past hundred years is a mooted one. Certain it 
is that there have been no marked changes. But 
there may have been minor ones, such as the falling 
of a portion of the wall of a crater, or the crumbling 
of some pinnacle. There is no trustworthy evidence 
of any volcanic outburst, great or small. Such an 
eruption as that at Krakatoa, which in 1883 gave rise 
to the red glows which persisted for many months, could 
not have escaped the scrutiny of astronomers. Craters 
change their appearance greatly as the sun rises upon 
them and causes their shadows to shift; hence very care- 
ful and prolonged study, comparing the old maps with 
present appearances, is needed to establish any claim of 
change. Now that photography has entered the field, 
and the sensitive plates make a record which is free 
from bias, it may be possible in the future to attain a 
good degree of certainty in this matter. 

When the moon parted company with the earth, ages Thelunar 
ago, it is probable that both masses were enwrapped in a atmos P h 
gaseous envelope. The lion's share of this atmosphere 
naturally fell to the earth, because of its superior attract- 
ive power. The moon may have started away with 
quite a scanty covering of air. It is natural then to 



ere. 



218 



A Study of the Sky. 



A star is 
hidden. 



Effect of 
refraction. 



suppose that the moon's atmosphere is now very rare. 
So clearly are the lunar mountains denned, so black are 
their shadows, so sharp is the dividing line between the 
illuminated and unilluminated portions of the moon, 
that there cannot be a dense envelope of air, which be- 
haves as ours does, scattering the sunlight in every direc- 
tion from the motes which float about in it, and causing 
twilight as the sun rises or sets. But a more delicate 
test is at hand. 

As the moon performs its monthly journey around the 
sky it passes between us and countless stars which seem 
to bestrew its pathway, but are really far beyond it in 
the depths of space. So well is the moon's rate of travel 
known that astronomers can predict accurately the time 
when it will hide any particular star from view. If 
there were a lunar atmosphere a star's radiance would 
be dimmed just before it disappeared ; it would also 
change color as the sun does at sunset, when it shines 
through a greater thickness of air than at noon. 

The mention of sunset brings to mind the fact that the 
air has a refractive power and bends rays of light which 
pass through it. On this account we see the sun after it 
is really below the astronomical horizon, and it appears 
again the next morning before it would, were there no 
air to bend its rays out of a straight course. 

A lunar atmosphere would therefore bend the rays of 
light from a star, and delay the time of its disappearance 
just as our air delays the time of sunset. It would also 
cause the star to reappear before it would otherwise. 
Thousands of occultations of stars by the moon have 
been accurately observed. The stars disappear and re- 
appear on time. 

The vacuum at the lunar surface is believed to be as 
complete as under the exhausted receiver of an air-pump. 



The Moon and Eclipses. 



219 



Several theories ^ r he ^ e h f s the 
The best 



What has become of the original aerial endowment 
which the moon probably possessed ? 
have been given to explain its disappearance 
of these is based upon observations on terrestrial rocks ; 
a rock which is heated expels gases which it had pre- 
viously absorbed ; when cooling, it has the power to take 
them up again. 




It may be that 
the lunar at- 
mosphere en- 
tered into chem- 
ical combination 
with the cooling 
rocks, and our 
satellite was 
thus stripped of 
its aerial ves- 
ture. 

No water is di- 
rectly revealed 
by telescopic 
search ; if it ex- 
isted the sun 
would evapo- 
rate it, and a 
slight lunar at- 
mosohere com- FlG> I04, — The Mare Crisium. 

posed of water vapor, would be formed. Since obser- 
vation has pronounced against the existence of a lunar water, 
atmosphere of appreciable density, it has also negatived 
the existence of water upon the moon's surface. Small 
bodies of ice may be there undetected, but there is no 
cogent reason for believing in their existence. Any 
water which the moon possessed originally may have 



220 A Study of the Sky. 

been taken up by the rocks as they crystallized, or may 
have sunk into cavernous depths in the interior. 

The absence of air has a marked effect upon the tem- 

a hot-bed. perature at the moon's surface. The gardener's hot-bed 

illustrates this matter. The sunlight pours through the 
glass cover of the bed and warms the soil within. The 
soil in turn strives to radiate off the heat which it has 
received, but the glass is a barrier to the returning heat. 
For heat from an intensely heated body passes through 
glass quite readily, while heat from a body at a low tem- 
perature, like the earth, finds difficulty in passing 
through glass. Therefore the gardener's bed becomes 
considerably warmer than the exposed ground round 
about it. 

In the same way our atmosphere keeps in the heat 

ket. which the sunbeams have brought to the earth' s surface ; 

the earth is kept warm by its blanket of air. For this 
reason the mean temperature on the top of a high moun- 
tain is much lower than that at its foot ; the top is cov- 
ered by a scantier blanket of air than the foot. Aero- 
nauts ascending to great heights experience bitter cold. 
Twenty miles above the earth's surface the temperature 
must be appallingly low. Were the atmosphere to be 
taken away, the sun would beat upon us more hotly 
than at present, but the beneficent heat would be quickly 
radiated off, and eternal winter would reign. 

Many attempts have been made to determine the tem- 

aturef mper " perature of the moon's surface by measurement of the 
heat which it sends to us. The moon's rays, condensed 
at the focus of a large mirror, fall upon a delicate in- 
strument for measuring changes of temperature. 
Though the results of various experiments differ, it is 
considered quite certain that the warmest portions of the 
lunar surface never rise above the temperature of freez- 



A visit to the 



The Moon and Eclipses. 221 

When some point has been in darkness for 
a week or more, the lunar nights being over two weeks 
in length, its temperature can scarcely be above — 200 
Fahrenheit. It has been estimated that the sun sends 
to the earth as much heat in a minute as the full moon 
would give could it shine upon us for three years without 
change of phase. 

The moon is a land of death, the sepulcher of any life 
which may once have existed upon it. If an astronomer moon 
could establish his telescope upon the rim of some great 
crater during a lunar night, and could endure the rigor 
of the cold, as well as the absence of air, what glories 
would rivet his astonished vision ! The sky, blacker 
than the deepest velvet, is inlaid with jewels unmatched 
by the gleam of a Koh-i-noor, or the splendid glow of 
the precious ruby. Each of the familiar constellations 
shines forth with a brilliancy before unknown. Not a 
star scintillates ; all shine serene, as though some high 
behest were upon them. A crowd of smaller stars, 
never before revealed to the unaided eye, besprinkle 
the sable folds of the garment of night. The Milky Way 
enchants the beholder by its splendor. Surely the char- 
iot of the Almighty has been driven along it. 

Amid this unchanging calm there is one magnificent 

1 .1 1 1-1 The earth is 

panorama. Yonder glows a mighty orb, which moves panorama. 

with majestic pomp amid the hosts of heaven ; star after 
star is quenched before it, and reappears in its wake. 
Steadily the sunlight creeps over its surface, changing 
it from a crescent to a full-orbed circle. While this 
change is taking place what a panorama rolls before the 
astronomer's eye, and is eagerly viewed with his tele- 
scope ! Great masses of white cloud, tinged with golden 
orange, vast expanses of ocean, dull continents relieved 
here and there by a dash of color, snowy masses at the 



222 A Study of the Sky. 

poles — all these roll before him, now glowing in the 
light, now lost in the darkness. 
Thedaycom»s. But what is the soft radiance which appears yonder 
upon the horizon ? Higher and higher it rises ; more 
and more is the lunar landscape lighted up. The 
ghostly shapes of distant mountains are dimly outlined. 
Long, black fingers stretch themselves across the 
plains ; thousands of dark pits dot the ashen landscape. 
The sun's long coronal streamers are heralding the 
dawn. Thoughtlessly he watches for the twilight, and 
expects to see the Milky Way veil its glories before the 
coming of the king of day ; but it shines on, with 
undiminished splendor. Behind him, on the opposite 
side of the crater, towers a precipitous pinnacle. Its 
rugged summit catches a ray of direct sunlight and is 
bathed in its effulgence. Yonder glows another peak 
and still another against the jet black sky. No rosy 
tints melt into amber, and suffuse the heavens. No 
lark soars to greet the rising sun, or to pour out his soul 
in ecstatic song. The silver-rimmed crater, standing on 
the dividing line between the world of light and the 
world of darkness, is filled with the shadow of its own 
wall. Deep down in its rugged depths are descried the 
heads of its central mountain, which are soon to be 
kissed by the sunlight. No laughing brook leaps down 
the mountain side ; no morning zephyr plays among 
the rugged battlements ; no flower turns its charming 
face toward the sun. 
The da r The day wears on ; the somber shadows move over 

declines. fa e desolate wilds. The rocky sentinels keep their 

grim and silent watch over the dead planet. Stray 
meteors dash against the beetling crags, or bury them- 
selves in the plains beneath. The life-giving sunbeams 
find no life responsive to their subtle touch. The 



The Moon and Eclipses, 



223 



shadows turn and lengthen ; the glowing sun sinks 
beneath the horizon, and the dread chill of the long 
lunar night comes on. 

The moon is of service to man in many ways. Its 
light relieves the darkness of the night, and this adds to 
his safety and happiness. As it moves across the face 
of the sky it becomes a timekeeper by which the 
mariner may determine his longitude, in case he is on a 
long voyage and fears that the error of his chronometer The mariner. 



The moon's 
worth to man. 




Fig. 105.— A Rugged Region near Tycho. 

is not known accurately. For the ' ' Nautical Almanac' ' 
gives the distance of the moon from certain bright stars 
at given Greenwich times, each day of the year. The 
mariner measures one or more of these distances with a 
sextant, and thus determines the true Greenwich time. 
The moon is the chief agent in the production of the 
tides, which at their flood lift ships over harbor bars 



The tides. 



224 



A Study of the Sky. 



Chronology, 



The ruse of 
Columbus. 



Superstitious. 



and bear them to the wharves. Without the tides the 
city of Liverpool would lose its commerce. Its harbor 
communicates with the ocean by a narrow neck, through 
which 600 million tons of water rush out every six hours 
during the ebb of the tide, scouring the channel, and 
carrying off the silt and debris which would otherwise 
choke it. 

Eclipses either of the sun or the moon, which occurred 
at the times of notable events, have given much assist- 
ance to historians in threading the mazes of ancient 
chronology. The lunar eclipse of March 13 in the year 
3 B. C. took place at the death of Herod, and thus 
serves to determine the date of the birth of Christ. 
Another eclipse has been employed to rectify the first 
year of the reign of Cyrus of Babylon. 

Columbus made use of the lunar eclipse of March 1, 
1504, to obtain much-needed supplies for his men. The 
inhabitants of Jamaica refused to give them to him, and 
he threatened to take away the moon's light should 
they persist in their determination. When the eclipse 
came on, the savages were struck with terror and has- 
tened to supply his wants. 

There have been many superstitions connected with 
the moon, some of which flourish even to-day in rural 
communities. Their absurdity is their sufficient refuta- 
tion. 

It has been said that the moon produces blindness by 
shining upon a sleeper's eyes ; that it Axes the hour of 
death, which occurs at the change of tide ; that cucum- 
bers, radishes, and turnips increase at full moon ; that 
onions thrive best after the moon has passed its full ; 
that herbs gathered before full moon are of greatest 
efficacy ; that vines trimmed at night when the moon is 
in the sign of the Lion are safe from field mice and 



The Moo?i and Eclipses. 225 

other pests ; that potatoes are best planted at a certain 
time of the moon ; that shingles will curl up if not laid 
at the right phase of the moon, etc., etc. 

Especially persistent are those ideas which connect 
the moon with the weather. A change of lunar phase the weather. 



is 



said to be connected with a change of weather ; since 



the moon changes its phase every week, every change 
of the weather must occur within four days of a change 
of phase. People who watch for such changes are will- 
ing to wait more than four days, if necessary, for the 
weather to accommodate itself to the moon. "Wet" 
and ' ' dry ' ' moons are carefully watched for by farmers 
throughout the country. When the crescent moon 
hangs low in the west soon after sunset, if a line joining 
the two cusps is nearly horizontal, so that the moon can 
apparently hold water, it is a "dry moon." If the 
line joining the cusps be tipped up at a very marked 
angle, so that the moon's crescent cannot hold water, 
the moon is called ' ' wet. ' ' The position of the cusps 
of the moon can be predicted for thousands of years to 
come, but no one can foretell the weather a week ahead. 

The full moon is said to clear away clouds ; it is hard clouds cleared 
to see how a body which sends us so minute a quantity awa y- 
of heat can have any appreciable effect upon the clouds. 
Perhaps by showing their thinness, and making plain 
the rifts which exist in them, the moon gets the credit 
of thinning them. 

That small variations in the position of the magnetic Mao . netic 
needle take place, as the moon approaches and re- eftecls - 
cedes, in pursuing its elliptical orbit, is admitted. 

ECLIPSES. 

Eclipses of the moon occur when it plunges into the ear h , 
shadow of the earth. If the sun were of the same size sh adow. 



226 A Study of the Sky 

as the earth, the shadow of the latter would be a 
cylinder, about 8,000 miles in diameter, stretching out 
to an infinite distance. But as the sun is much larger 
than the earth, the shadow is tapering. Its length 
varies somewhat, since the earth is sometimes farther 
away from the sun than at others. Its average length is 
857,000 miles, and its average thickness, at the point 
where the moon encounters it, is 5,700 miles. The 
moon often merely dips a little way into the shadow, 
and suffers only a partial eclipse. Being only 2,163 
miles in diameter, it is readily totally eclipsed, and may 
remain immersed in the shadow for two hours. 

Since the moon moves eastward, its eastern edge, 
a lunar eclipse, which is at the left hand as one faces it, strikes the 
shadow first ; a circular notch then seems to be eaten 
out of the moon's edge, much as if it were an apple out 
of which a boy had taken a bite. The notch increases 
till the lunar disc is overspread with shadow, but the 
moon does not usually disappear. The solid body of 
the earth casts a shadow sufficiently dense to blot the 
moon out as completely as if it were annihilated, but the 
transparent coating of air which the earth carries assists 
the moon in its otherwise gloomy experience. Many 
rays of sunlight pierce this transparent medium, are 
bent by it out of their otherwise straight course, and fall 
upon the moon, illuminating it rather dimly because they 
have been enfeebled by passing through our atmosphere. 
They have also acquired the sunset tinge, and give the 
moon a coppery-red hue. If clouds stop these rays, 
the moon vanishes entirely ; if, on the other hand, the 
portion of the atmosphere traversed by them is excep- 
tionally free from moisture, the lunar disc is lighted up 
so strongly that persons unaware of the eclipse simply 
wonder why the moon is not as bright as usual. After a 



228 



A Study of the Sky. 



The moon's 
shadow. 



A solar eclipse. 



while the eastern edge of the moon emerges into sun- 
light and the shadow is gradually left behind. 

Since the moon's diameter is a little more than one 
fourth that of the earth, and their distances from the 
sun are nearly equal, the moon's shadow is somewhat 
more than one fourth as long as the earth's. Its length 
varies because of changes in the moon's distance from 
the sun, caused chiefly by the varying distances of the 
earth, which carries the moon along with it. When the 
moon is between the other two bodies, its shadow is at 
times too short to reach the earth ; at other times it is 
long enough and makes a small dark spot on the earth's 
surface. Since the moon is continually in motion, the 
shadow travels eastward over the earth ; the earth is 
turning in the same direction. If the shadow is now 
falling on the city of New York, there is a race between 
the city and the shadow ; but the latter is the swifter 
and passes out upon the Atlantic. A shot from a rifled 
gun would keep it company for a brief space of time. It 
is not often more than 150 miles in diameter, and cuts a 
pretty small swath on the earth's surface. 

Any one who establishes himself within the limits of 
the swath may see the sun totally eclipsed, if the sky be 
clear, during the time occupied by the shadow in pass- 
ing over him. An observer near the path of the shadow 
may see the sun partially eclipsed. On rare occasions 
there is an interrupted view of the corona and promi- 
nences for six or eight minutes before the brilliant 
photosphere peeps out at one edge of the retreating 
moon, and floods the landscape with light. Ordinarily 
the sun is entirely covered for only two or three minutes. 

A total solar eclipse is one of the most awe-inspiring 
phenomena of nature. The approach of the moon, 
which quietly eats its way into the solar disc, is not no- 



A total solar 
eclipse. 



The Moon and Eclipses. 229 

ticed by those who are uninformed. For the sunlight is 
so piercing that no special diminution of it is perceived 
until the eclipse is well advanced. At last the light be- 
gins to pale, as though a haze were forming over the sun. 
One who takes a quick upward glance, or employs a 
dark glass, sees that the sun is now a narrow cres- 
cent. The supreme moment is at hand ; the landscape 
assumes an unearthly hue. The beholders are silent and 
stricken with awe. One stationed on a mountain may 
see the shadow advancing over the plain below with ap- 
palling speed. In but a moment it has come ; the moon 
hangs in mid-heaven, a ball of inky blackness, fringed 
with blazing prominences, and enveloped by the silvery 
corona. The moments are counted by heart-beats. The 
planets and brighter stars bedeck .the sky ; perchance a 
stray comet peers forth in the sun's vicinity. The up- 
turned faces of the onlookers are ghastly. A piercing 
ray of light springs from the edge of the moon ; the 
prominences are gone. The corona fades away ; the 
stars return. The landscape glows with the returning 
light. The sublime spectacle is over. 

It has not been without curious effects upon the lower 
orders of creation. The convolvulus closes its leaves, plants and 
birds cease flying, chickens go to roost, beasts leave 
their food, bees return to the hives, caged birds die of 
fright or thrust their heads under their wings, crickets 
sound their nocturnal notes, bats fly about ; some horses 
seem to be overcome with fright and sink down in the 
street ; others are blind to the changes about them, and 
go on without even pricking up their ears. Oxen have 
been known to arrange themselves in a circle, heads out- 
ward, as if fearing attack. 

Among semi-civilized or savage nations a solar eclipse 
inspires great terror. Hindus believe that a great 



animals. 



Superstitious 
terror. 



230 



A Study of the Sky. 



Work during 
an eclipse. 



Small planets. 



dragon is striving to devour the sun. They fill the air 
with unearthly screams and shouts, and beat their gongs 
fiercely ; the monster must be frightened away. Great 
is their joy when the voracious jaws eject the scorching 
morsel. 

We have gone far afield, and must return to summa- 
rize briefly some of the work which modern astrono- 
mers attempt during the fleeting moments of a total 
solar eclipse. 

I. The prominences and corona are observed tele- 
scopically. 

II. Spectroscopic observations are made of the co- 
rona, the protuberances, and the chromosphere. 

III. The light of the corona is studied with the polari- 
scope ; the purpose is to determine the relation between 
the light which the coronal particles reflect and that 
which they emit because of their incandescence. 

IV. A search for possible small planets revolving in 
the neighborhood of the sun, and usually hidden by its 
glare, is prosecuted. Reports of the discovery of such 
bodies have been the subject of rather acrimonious dis- 
cussion. Professors Watson and Swift announced such 
discoveries during the eclipse of July 29, 1878, but no 
similar observations have been made at any succeeding 
eclipse. 

V. Photographs of the corona and of the prominences, 
being more trustworthy than hurried drawings, are much 
in voeue. 



CHAPTER XIII. 

MERCURY AND VENUS. 

' Lo ! in the painted oriel of the West, 
Whose panes the sunken sun incarnadines, 
Like a fair lady at her casement, shines • 
The evening star, the star of love and rest." 

— Longfellow. 

Mercury and Venus are denominated inferior plan- inferior 

ets because their distances from the sun are less than P lanets - 
that of the earth. 

They are in conjunction when they appear to us to be _ . 

J , , Conjunction. 

nearly in line with the sun ; the word conjunction sug- 
gests this. An ijiferior conjunction of Mercury or 
Venus occurs when the planet is between the sun and 
the earth ; a superior conjunction takes place when the 
planet is beyond the sun. When at inferior conjunction 
a planet may come so near a line joining the centers of 
the earth and sun that it is seen against the background 
of the solar disc as a small black circle moving across its 
face. It is then in transit. After an inferior planet 
passes inferior conjunction it moves out toward the 
right as we stand facing the sun ; it is then west of the 
sun, rising and setting before the sun does each day. In 
Fig. 107 S is the sun and E the earth, while the circle 
represents the orbit of Venus. When Venus is at C it 
is in inferior conjunction. It then moves toward V, get- 
ting further and further to the right of the sun each 
week. When at V it has attained its greatest apparent 
distance west of the sun, and is at its greatest western 



232 



A Study of the Sky. 



Elongation. 



Morning and 
evening star. 



Phases. 



elongation. When moving from V toward C it appar- 
ently approaches the sun. C is the point of superior 
conjunction. After passing C Venus is at the left of the 
sun, rising and setting after the sun does. V is the 
point of greatest eastern elongation. After passing V 
the planet swings back toward the sun. 

In this explanation we have tacitly assumed that the 

earth is at rest ; in reality 
it is moving in the same 
direction as Venus, but 
more slowly. This simply 
lengthens the time which 
elapses between inferior 
conjunction and greatest 
western elongation, or be- 
tween any two of the 
positions which we have 
just defined. 

Greatest western elon- 
gation really comes when 
Venus has arrived at V", 
the earth meanwhile having moved on to E\ When an 
inferior planet is west of the sun it is a morning star ; 
when east of the sun it is an evening star and is to be 
looked for in the west. 

Since Mercury and Venus shine by reflecting the sun- 
light, and have no intrinsic radiance, they exhibit phases 
similar to those of the moon. At inferior conjunction 
the dark side of the planet is toward us ; as the planet 
moves out toward western elongation its phase is a cres- 
cent like that of the young moon. 

At greatest elongation the phase is a semicircle, like 
the moon at one of its quarters. When the planet is at 
superior conjunction we look full in its illuminated face, 




Fig. 



[07.— Conjunction and Elon- 
gation. 



Mercury and Venus. 233 

which is a complete circle. Afterward it descends 
through the gibbous phase, to a semicircle, and thence 
to a narrow crescent again, as it approaches inferior 
conjunction. 

Of Mercury little is known, for it is coy and keeps Mercur 
close to the sun. The most favorable times for seeing it 
in the evening are those when it reaches its greatest 
eastern elongation in March or April. For it is then 
nearly above the sun at sunset ; at such a time it may be 
seen every night for two successive weeks, one of which 
immediately precedes the time of elongation. It is then 
very plain, even in strong twilight, and is not likely to 
be confounded with any fixed star. 

Its mean distance from the sun is 36,000,000 miles. Its distance. 
Its orbit is more eccentric than that of any other of the 
large planets, so that its actual distance from the sun 
ranges from 28,500,000 to 43,500,000 miles. 

Sunlight upon Mercury is more than twice as intense T . ., , 

or j Intensity of 

when it is nearest the sun as when it is farthest away. sunli §: ht - 
The average intensity is seven times that which we ex- 
perience. The diameter of the planet is 3,000 miles, 
and eighty-eight days are consumed in making a revo- 
lution about the sun. 

It is very difficult to make out any markings on Mer- 
cury's disc. The Italian astronomer, Schiaparelli,* 
whose observations of the canals of Mars have proven 
that he is exceptionally keen of sight, has observed cer- 
tain dim and ill-defined spots whose motion renders it 
probable that Mercury rotates on its axis in eighty-eight 
days, and thus presents the same face continually to the 
sun. 

There is great uncertainty about the presence of air or Air, water, 
water ; certain spectroscopic observations indicate that 

* Astronomer at Milan, Italy. 



Rotation. 



and mountains. 



234 



A Study of the Sky. 



Venus. 



Revolution 
and rotation. 



Shadings. 



Ice and snow. 



there may be a thin atmosphere, in which water vapor 
is present. If these be accepted as correct, the dim 
shadings described by Schiaparelli may be the outlines of 
seas or continents. 

One imaginative astronomer discovered mountains on 
the planet about a century ago. Though his telescope 
was a pigmy compared with those of to-day, modern 
observers have not verified the existence of the moun- 
tains. 

VENUS. 

Venus is a more interesting object than Mercury be- 
cause it comes nearer to us and is larger and brighter, 
giving more light than any other planet. Its distance 
from the sun is 67,000,000 miles, and its orbit is nearly 
a circle. It is almost as large as the earth, having a 
diameter of 7,700 miles. 

Two hundred and twenty-five days are consumed in 
making a revolution about the sun. The time of rota- 
tion is generally given as about twenty-four hours, this 
period having been derived from old observations, 
which have received some confirmation in recent times. 
Schiaparelli' s investigations cast discredit upon this 
value, and tend to show that Venus, like Mercury, 
keeps the same face toward the sun. 

Many astronomers have seen shadings upon the 
planet's surface, but they are so ill defined that their 
cause is unknown. When the planet is a crescent, the 
horns are brighter than the rest of the surface. Possi- 
bly ice and snow at the planet's poles cause this appear- 
ance. On the whole, it may be said that telescopic 
scrutiny of Venus has decided nothing as to the con- 
figuration of its surface. 

It seems to be covered with a dense atmosphere, 
which is an effectual bar to our curiosity. The existence 



Mercury and Venus. 



235 



of the atmosphere is shown at the times of its transits. 
When Venus is just about to enter upon the sun's disc, 
or has just passed off, it is surrounded by a tiny rim of 
light. The sunlight has — ~ — - — 

pierced through the planet's / "^^V 

atmosphere and come on to our / \ 

eyes. It is probable that the / \ 

atmosphere is denser than our f ,.,; ; | 

own, but not more than twice 1 \ 

as dense. The spectrum con- 
tains lines which indicate the / 
presence of water vapor. It is 7 
a reasonable inference that 
Venus is a planet whose sky is 
almost totally cloudy, and 
whose atmosphere is continu- 
ally laden with moisture. On 
a day when the entire earth is enveloped in a cloud- 
shell, to an inhabitant of the moon it would present, on 
a huge scale, the appearance of Venus. 



Fig. 108.— Markings on 
Venus. 



Atmosphere. 



Mars. 



Perplexities. 



CHAPTER XIV. 

MARS AND THE ASTEROIDS. 

" And earnest thoughts within me rise, 
When I behold afar, 
Suspended in the evening skies, 
The shield of that red star." 

— Longfellow. 

Mars is perhaps the most interesting planet, because 
of the tantalizing chase on which he has led observers. 
He is at times almost as near as Venus when the latter 
is in inferior conjunction ; yet he is even then so far 
away that the more delicate features of his surface, like 

the canals, are seen 
with great difficulty, 
and are the source 
of much perplexity. 
Even the marked 
features which have 
for generations 
passed unchal- 
lenged under the 
names of continents 
and seas are now 
subjected to rigid 
scrutiny, and in 
fig. io 9 .— Mars. some quarters are 

denied their time-honored appellations. While there is 
a fair consensus of opinion as to the majority of appear- 
ances seen upon the planet, there is considerable diver- 




The orbit. 



Mars and the Asteroids. 237 

sity in the interpretations which are put upon them. 

In considering such a subject one must maintain a 
judicial frame of mind, realizing that while conservatism nXd. 101 ' 
is generally to be preferred to rashness, yet the age of a 
theory should not shield it from searching examination, 
as the novelty of a result should not debar it from the 
most candid treatment. 

The mean distance of Mars from the sun is 141,500,- 
000 miles. His orbit departs farther from the circular 
form than that of any other planet save Mercury. The 
difference between his greatest and least distances 
from the sun is 26,000,000 miles. He is best seen 
when the earth lies between him and the sun ; we are 
then nearer to him than at other times, and he appears 
bigger and brighter. 

At such a time if he happens to be near perihelion, 

, . . . . f . . . . . Perihelion and 

which is the point 01 closest approach to the sun, and the aphelion, 
earth is near its aphelion^ which is the point of furthest 
recession from the sun, the distance between the two 
bodies is but 36,000,000 miles. This close approach 
occurs every fifteen years, and took place in August, 
1892, for the last time during the nineteenth century. 

All those planets whose orbits are larger than that of 
the earth are called superior planets. When the earth is pianetsf 
nearly in a line between a superior planet and the sun, 
so that the former appears to be on the opposite side of 
the celestial sphere from the sun, it is said to be at 
opposition. When the planet is beyond the sun and 
nearly in line with it, it is in conjunction. When Mars 
is at a favorable opposition it is more than fifty times as an°d J oppSon. 
bright as at conjunction, and rivals Jupiter in splendor. 
When far from opposition it might readily be mistaken 
for a red fixed star, did not its motion betrav its true 
character. 



2 3 8 



A Study of the Sky. 



Diameter, 
revolution, 
rotation. 



and 



The moons. 




The diameter of Mars is 4,200 miles. It consumes 
687 days, or nearly twenty-three months, in making one 
revolution about the sun. Some of the markings on its 

surface are so well 
denned and stable 
that the time of ro- 
tation has been 
found very accu- 
rately by comparing 
drawings made in 
the seventeenth cen- 
tury with modern 
ones. The received 
value is 24 hr - 37 min - 
22.67 sec - The ro- 
tation axis of the 

Fig. iio. — Projections on the Polar Cap. planet IS not perpen- 
dicular to the plane of its orbit, but deviates 27 ° from 
that position. Therefore there must be seasonal changes 
on Mars just as on the earth. 

Two tiny moons attend the planet ; they were discov- 
ered at the favorable opposition of 1877 by Professor 
Asaph Hall.* Their names, Deimos and Phobos, are 
translations of Greek words used by Homer as designa- 
tions of the fiery steeds which drew the chariot of 
the god of war. They are the smallest known bodies in 
the solar system, with the exception of meteors. Dei- 
mos occupies 3o hrs - i8 min - in making one revolution, and 
is 12,500 miles from the planet's surface. From meas- 
ures of its brightness its diameter has been estimated at 
five or six miles. Phobos, the inner moon, is only 3,700 
miles from the surface of Mars ; it accomplishes a revo- 



* Then an astronomer at the United States Naval Observatory at Washing- 
ton ; now on the retired list. 



Mars and the Asteroids. 



239 



luti 



,hr. 



39 



and is the only known moon which 



A quick trip. 



makes the trip around its primary in less time than the 
primary takes to turn once on its axis. In consequence 
of this unusual speed it rises in the west and sets in 
the east. A man living near one of the poles of Mars 
would never see Phobos, because it revolves in the plane 
of the Martian equator, and keeps close to the planet. 
To us they seem to fill the office of nocturnal luminaries 
very imperfectly, the light given by Phobos to possible 
Martians being but one sixtieth of our moonlight. Dei- 
mos sheds upon 
Mars only one 
twentieth as much 
light as Phobos. 
They go through 
the. same phases as 
our own moon.* 

The planet itself 
is subject to changes 
of phase. At op- 
position, when the 
earth is between the 
sun and Mars, the 
latter exhibits a full, 
round disc, as we 
are directly in front of its illuminated hemisphere; at Phasesofthe 
conjunction it has the same phase, but at intermediate P lanet - 
times we cannot see all of the bright hemisphere. 




Fig. hi. — The Lake of the Sun 



* The discovery of these satellites was curiously anticipated by Kepler, 
Dean Swift, and Voltaire. One of Kepler's strange speculations, which he 
mentioned in a letter to Galileo, was that Mars had two moons, Saturn six or 
eight, while Mercury and Venus were possibly blessed by a single attendant 
each. Dean Swift represents in " Gulliver's Travels " that the scientific Lilli- 
putians had telescopes of great power, with which they had discovered "two 
lesser stars or satellites which revolve about Mars." Voltaire makes a hypo- 
thetical inhabitant of Sirius take a celestial voyage, in the course of which he 
visits Mars and sees two moons which are intended to make up for the compara- 
tive feebleness of the sunlight. 



240 A Study of the Sky. 

The most conspicuous appearances on the face of 
The polar caps. Mars are roundish white masses at the poles. They were 
plainly seen soon after the invention of the telescope, 
and have been observed ever since. Neither one of 
them maintains a uniform size. When summer reigns 
in the northern hemisphere of the planet the white area 
around the north pole diminishes and almost vanishes ; 
when summer yields to winter the white spot grows 
again. In October, 1894, tne south polar spot became 
so small that many astronomers believed that it had van- 
ished. But the Lick telescope, under the manipulation 
of Professor E. E. Barnard, still showed it, though with 
great difficulty ; it was very small, and seemed to be 
partially obscured by an overhanging veil. The polar 
caps are supposed to be composed of snow and ice. 
Most of the planet's surface is of a yellowish-red 
surfa?e? eral color ; the remainder is usually of a dark gray tint. 
Many maps have been made, which agree quite satis- 
factorily in their main details. The yellowish-red re- 
gions are thought to be dry land ; the dark gray regions 
bodies of water. 
The canal Fig"- 112 exhibits several of the canals. Schiaparelli 

was not the first astronomer to notice them : some 
were observed by several distinguished astronomers be- 
fore his day. But he has found so many that they are 
by common consent called " Schiaparelli' s canals." No 
other observer, however large his instrument, has com- 
pletely verified the mysterious network with which 
Schiaparelli' s map is covered.* The majority of the 
canals are several hundred miles long. A canal occa- 
sionally appears to be doubled ; that is, a new canal 



* However, Mr. Percival Lowell, and the observers associated with him, at 
Flagstaff, Arizona, have mapped a large number of canals not detected by 
Schiaparelli. An account of these is given in Mr. Lowell's book entitled 
" Mars." 



Mars and the Asteroids. 



241 



appears running by the side of the old one. Schia- 
parelli states that this duplication is probably periodi- °°^5s ing ° f 
cal, and has some connection with the changes of the 
seasons. Several canals often meet at a point, as 
though they were spokes radiating from a hub. They 
are the most mysterious objects on Mars, and a host of 
theories have been broached about them. Schiaparelli 
has suggested that they may be natural water-ways 




Fig. 112.— Canals. 

through which the waters caused by the melting of the 
polar snows flow toward the equator. 

There are other more transient appearances. Some- 
times there are small spots of tolerably definite outline 
which are visible for a time and then vanish. At other 
times there are large diffuse patches, which seem to 
obscure the familiar outlines shown on the map. Both 
of these appearances may be ascribed to clouds. Large 
reddish areas now and then have a whitish aspect, as 
though snow had fallen upon them. One small orange 
spot has often appeared white : perhaps it is a moun- 



Clouds and 
snow. 



242 



A Study of the Sky 



Inundations. 



Melting of 
a cap. 



tain or high table-land, where snow falls readily. Pro- 
jections like saw-teeth are seen on the edge of the disc. 
Some of these may be large clouds floating high in the 
atmosphere of Mars ; others may be due to mountains. 
Large dark regions extend their boundaries, and 
seem to obliterate adjoining yellowish ones. After 
several weeks or months they resume their usual form. 




Fig. 



-Projections on the Edge of the Disc. 



If lowlands adjoin a sea, their inundation would cause 
such changes of appearance. 

When a polar cap is diminishing, a dark rim has 
been seen about it, as if it were bordered by the water 
coming from the melting cap. In 1892 the south polar 
cap dwindled very rapidly, and there were very inter- 
esting changes in its vicinity. It lost 1,500,000 square 
miles of its area in a month. At first a dark spot 



Mars and the Asteroids. 



243 



appeared in the midst of the cap ; it gradually enlarged 
and cleft the cap in twain. A part of the region be- An overflow. 
tween the diminished cap and one of the well-known 
dark portions of the disc became dark, and then the 
dark region just mentioned was enlarged, intrenching 
upon the adjacent lighter regions. All of this is readily 
explained on the assumption that the first dark spot 
within the polar cap was water, which had been pro- 
duced by the melting of the snow and ice. If this snow- 
water found its way across lowlands to an adjacent 
sea, and caused the latter to overflow its boundaries, 
the phenomena which followed the melting of the polar 
cap in 1892 are explained. 

There is one dark spot called Lacus Solis, the Lake LacusSoiis. 
of the Sun, which is 



every op- 
It is sur- 



plain at 
position 

rounded by a bright 
ring, which, accord- 
ing to our previous 
theorizing, is dry 
land. Sometimes 
the ring is wide and 
conspicuous; at 
others it is narrow 
and not easily seen. 
A large dark spot, 
thought to be an 
ocean, is near at 
hand ; at times canals connect the 
traversing a portion of the bright 
there is a break in the bright rii 
like a horse-shoe, the vanished 
bright ring being dark ; the 




Fig. 



114.— Canals Connected with Lacus 
Solis. 



lake with the ocean, 

ring ; at other times 

ing, which then looks 

portion of the original 

lake and the sea are ap- 



A horse-shoe. 



244 



A Study of the Sky. 



The canals fill. 



Various 
theories. 



Irrigation. 



parently joined. If the land separating the lake from 
the sea is low, and slight changes in the water level 
are admitted, the preceding changes in appearance may- 
be explained. When the water is low the bright ring is 
complete ; when it is a little higher it fills the canals ; 
when it is still higher it inundates the portion of the 
bright ring lying between the two bodies of water. 



/ 




Fig. 115. — The Polar Cap in July and August, 1892. 

Plausible as all the theories about snow, seas, dry 
land, clouds, and inundations, which have been ad- 
vanced, may appear, we must not forget that they are 
all subject to revision when new light is obtained. The 
most variant theories have already been proposed. It 
has been suggested that the polar caps are simply 
masses of cloud ; that the bright portions of the planet's 
surface may be water, while the dark ones are land ; 
that the doubling of the canals is an illusion ; that the 
canals are not to be considered as water-ways, but as 
streaks of vegetation bordering upon streams which are 
themselves too narrow to be seen. One writer says 
that the canals are so straight and so well distributed 
over the planet's surface that they may be considered 
as the work of intelligent beings, who use them for 
purposes of irrigation. Another remarks that they are 
indefinite shadings, vague in outline, and often discon- 
tinuous. 

The popular interest in Mars has arisen largely from 



Mars and the Asteroids. 



245 



the possibility that it is habitable by human beings. 
Practical astronomers generally look upon such specula- 
tions with ill-disguised disdain ; let us examine into the 
matter for a moment. If there be land and water, and 
freedom from disastrous inundations, in certain regions, 
a man would simply need an atmosphere like our own, 
and a suitable supply of warmth, together with a fertile 
soil. 

What has been determined concerning the atmos- 
phere? If it were as dense as our own, and of similar 
composition, we could not see the polar caps and other 
prominent features so distinctly. The color of the caps 
would be altered from white to a reddish tint, since we 
always see them obliquely through quite a thickness of 
atmosphere. Furthermore the spectrum of Mars should 
contain strong absorption bands if the atmosphere were 
dense. More than one European astronomer, using a 
comparatively small instrument, has found spectroscopic 
evidence of the existence of water vapor in the planet's 



Habitability. 




The atmos- 
phere. 



Fig. 116. — Canals in August, 1892. 

atmosphere. But Professor Campbell,* with a large 
spectroscope attached to the great Lick telescope, found 
no evidence of water vapor, and sees no absorption 
bands whatever. In his opinion such bands would have 
been evident if the atmosphere of Mars were one fourth 
as dense as our own. A man therefore would gasp and gasp and die. 

* Of the Lick Observatory. 



246 A Study of the Sky. 

die, if Professor Campbell's conclusions are to be ac- 
cepted. 

The climate of the planet seems to be mild ; else why 
should the polar snows melt so rapidly and cause fresh- 
ets ? The sunlight which reaches Mars is less than half 
as intense as ours. 

If its atmosphere be rare, why has it such a power of 

the atmosphere, imprisoning the sunbeams and keeping the planet warm ? 

Are we not led by this course of reasoning to suspect 



A warm cli 
mate. 



Composition of 




W/ 



Caution. 



Fig. 117. — The Cap Diminishing, August 24-29, 1892. 

that the composition of the Martian atmosphere is widely 
different from that of our air ? Would not a human 
being fare ill on Mars ? 

While the basis of our argument is confessedly slen- 
der, and the conclusions may be wide of the facts, does 
not the best light available indicate that Mars is prob- 
ably not a suitable place for human habitation? We 
cannot deny that our neighbor may be inhabited ; its in- 
habitants may be far superior to mankind, in both phys- 
ical and mental endowments. But such speculations are 
no part of the science of astronomy. 

THE ASTEROIDS. 

In the year 1772 Professor Johann Titius, of Witten- 

An arithmetical . . 

scheme. berg, devised an arithmetical scheme for representing 

the relative distances of the planets from the sun. By 
adding four to each of the numbers o, 3, 6, 12, 24, 48, 



Mars a?id the Asteroids. 247 

and 96, he obtained a series which approximately repre- 
sented the data. If we represent the earth's distance 
by 10, the correspondence between theory and fact is 
shown below : 

Theory. Fact. 

Mercury 4 3.9 

Venus 7 7.2 

Earth 10 10. o 

Mars ' 16 15.2 

28 

Jupiter 52 52.0 

Saturn 100 95.4 

The gap between Mars and Jupiter made a profound The gap 
impression upon Bode, a Berlin astronomer, and he 
boldly predicted that a planet would some day be found 
which would fill out the series. The discovery of 
Uranus in 1781 at a distance agreeing fairly with the 
next term of the series gave a powerful impetus to the 
idea that there must be a planet between Mars and 
Jupiter. 

Half a dozen German astronomers formed an associa- Celestial police, 
tion of celestial police to search for the truant planet. 
Before these officers had gotten their belts fairly tight- 
ened up, a Sicilian astronomer, Piazzi by name, caught 
sight of the missing body. 

He was engaged in the somewhat prosaic work of The discovery. 
making a star catalogue, and had observed the right 
ascensions and declinations of a large number of stars. 
On January 1, 1801, the first evening of the century, he 
observed the position of a star of the eighth magnitude ; 
on the next night he observed it again. The two obser- 
vations did not agree. The third night he tried it, and 
encountered another disagreement. He was satisfied 
that it was in motion, and observed it for six weeks, 
until a serious illness seized him. 

Meanwhile he had written letters to Bode and another 



248 



A Study of the Sky. 



Delayed letters. 



Gauss. 



astronomer, telling of his good fortune ; but there were 
no express trains in those days, and the letters tumbled 
about for a couple of months before they reached their 
destinations. It was then too late to look for the new 
body, for the sun had gotten around into that part of 
the sky. The celestial police took extra hitches in their 
belts and ruminated, but their ruminations were of no 
avail ; not one of them could find out where to look for 
the fugitive, after the sun had passed by. 

A rising young mathematician, Gauss by name, who 
afterward became one of the foremost of astronomers, 
set himself at work on the problem and unraveled the 
hard knots in it. By November he was able to tell the 
celestial police (as they called themselves) where to 
hunt. The clouds and storms of winter now baffled the 
searchers. But on the last day of the year the fugitive 
was caught. AtPiazzi's request it was named after one 
of the lesser divinities, Ceres, the tutelary goddess of 
Sicily. 

Three months afterward Olbers, of Bremen, chanced 
other asteroids, upon a similar object, which proved to be another small 
planet, revolving in an orbit of nearly the same size as 
that of Ceres. To it the name Pallas was given. 
Within half a dozen years two more, Juno and Vesta, 
were captured. The progress of discovery was slow up 
to 1850, when about thirteen were known. 

The method of search was laborious, but easily under- 
stood. Star charts were constructed, showing all stars 
(except the very minutest) visible in certain regions of 
the sky. Night after night the charts were compared 
with the heavens to see if any object not on the chart 
was in evidence. Whenever a faint star-like object was 
found to be in motion, it was hailed as a new minor 
planet, observed with diligence, enchained by the toils 



The old method 
of search. 



Mars and the Asteroids. 249 



of mathematics, and finally imprisoned in an astronomi- 
cal almanac. 

Nowadays astronomers hunt this sort of game with a The new 
camera, which is attached to a telescope of short focal method - 
length, having a large field of view. The image of each 
star photographed is a tiny point on the sensitive plate. 
The photographic signature of an asteroid differs from 




Fig. 118. — Asteroid Trail on a Photograph of the Pleiades. 

that of a star ; since it is in motion with reference to the 
surrounding stars, its image on the plate moves, produ- 
cing a short streak. When the plate is developed the 
astronomer soon discovers this anomalous mark among 
the other little dots, and knows that he has photographed 
an asteroid, new or old. 

A " Rechen Institut" in Berlin, composed of astro- who takes 
nomical computers, takes care of these members of the 



care of them? 



250 



A Study of the Sky. 



Their orbits. 



Their sizes. 



sun's family, sifts out the new ones from those previously 
known, computes their orbits, predicts their places 
from year to year, and calls attention to those whose 
orbits are not yet securely determined, so that they 
may be observed afresh before they are lost. They now 
(1896) number over 400, and are being discovered too 
rapidly for the comfort of the computers who have them 
in charge. By the end of the nineteenth century five or 
six hundred of them will probably be known unless the 
zeal of certain astronomical photographers is checked. 

The mean distances of the known asteroids range from 
200,000,000 to 400,000,000 miles, and their periods of 
revolution from three to nine years. A few of them ap- 
proach so near Jupiter as to surfer considerable perturba- 
tions by their giant brother. One of them is sometimes 
nearer the sun than is Mars. Despite the great entan- 
glement of the various orbits, there is no special danger 
of collision, except on the part of Fides and Maia, which 
may become united into one body or become a system 
like the earth and moon. 

Vesta is the brightest and is occasionally visible to the 
naked eye. The diameters of four of them have been 
measured by Professor Barnard with the Lick telescope 
with the following results : 

Ceres 485 miles. 

Pallas 304 miles. 

Juno 118 miles. 

Vesta 243 miles. 

Their faintness indicates that most of them do not ex- 
ceed fifty miles in diameter. Those which are discov- 
ered by photography are, as a rule, decidedly insignifi- 
cant, many of them having probably as small a diameter 
as ten miles. Five hundred of them together would be 
only a millionth as large as the earth. 



Mars and the Asteroids. 251 

A man would be much interested in paying a visit to 
one of these tiny worlds, if he could get along without a S Sroid° a " 
his usual supply of air, and endure the rigors of cold 
which obtain there. If the asteroid were composed of 
as dense materials as the earth, and were only eight 
miles in diameter, the force of gravity at its surface 
would be one thousandth as great as on the earth. A 
baby who tosses a ball to a height of five feet could there 
toss the same ball a mile. The man could throw a base- 
ball clear off the planet. Should he essay to walk, the 
first spring of his ankle would project him upward off 
the ground. An attempt at running would be a ludi- 
crous series of one-legged leaps. Should he leap off a 
cliff 1,000 feet high, he would reach the bottom in a lit- 
tle over four minutes, and would experience no more 
severe a shock than if he had jumped down a space of 
one foot on the earth. If he tried to sit down, his feet 
would be lifted off the ground, and he would gently fall 
into his seat. If he lifted up a basket of eggs with no 
more care than he would take on the earth, the eggs 
would leave the basket, rise about 140 feet, and return 
in three minutes and a fraction.* 

At first it was supposed that the asteroids were frag- Qri in ofthe 
ments of a larger planet, which had been shattered by ast eroids. 
an explosion. If this were the case, the orbits of all the 
fragments would at first intersect at the point where the 
explosion occurred. The disturbances caused by the 
attractions of the other planets would so alter the differ- 
ent orbits that after a few thousand years they would 
be very far from meeting at any given point. The 
changes which a few of the orbits have undergone in the 
past have been approximately ascertained, and no clue 
to a common point of intersection has been found. The 

* These calculations are based on an initial velocity of three feet a second. 



252 A Study of the Sky. 

hypothetical explosion must have occurred hundreds of 
thousands or millions of years ago, if ever. 

According to the nebular hypothesis (to be set forth 
a ring of hereafter), the asteroids may have arisen from the con- 

densation of a ring of nebulous matter, which was left 
behind, as the original solar nebula contracted. This is 
the commonly received explanation of their origin. 



CHAPTER XV. 

JUPITER, SATURN, URANUS, AND NEPTUNE. 

" Some displaying 
Enormous liquid plains, and some begirt 
With luminous belts, and floating moons, which took, 
Like them, the features of fair earth." 

— By r on. 

Jupiter is the giant of the sun's family of planets. 
The distance from pole to pole is over 84,000 miles. At dimensions 
the equator his diameter is nearly 90,000 miles. He is an s ape * 
therefore decidedly out of round. The elliptical shape 
of his disc is readily perceived with a telescope, or in 
any good picture of him. So marked an equatorial 
bulge may be due to one or both of two causes. He 
may rotate with extreme rapidity, so that the ' ' centrif- 
ugal force" at the equator is large, or he may be so 
plastic that even a low velocity of rotation would cause 
the bulging observed. As we shall see presently, there 
is good reason to believe that both of these causes 
operate. 

His bulk is 1,300 times that of the earth ; all the 
other planets compacted together into one would not 
equal him in volume. His mean distance from the sun 
is 483,000,000 miles, which is more than five times the 
earth's; 11.86 years are occupied in one revolution 
about the sun. 

Like all other superior planets he is brightest at 
opposition, attaining then a luster which exceeds that of ance 
any other planet except Venus ; at such a time he casts 



Size, distance, 
and time of 
revolution. 



His appear- 



254 



A Study of the Sky, 



Rotation. 



The belts. 



perceptible shadows of terrestrial objects. Many spots 
can be seen on his surface, even with a telescope of 
moderate power ; by watching their motion the time of 
rotation has been determined ; it is about 9 hrs - 55 min " 




Fig. 119.— Jupiter. 

The swiftness of rotation makes the delineations of its 
surface markings difficult. 

In a small telescope dark belts parallel to the planet's 
equator are plainly contrasted with the general yellowish- 
white background. A large telescope reveals a wealth 
of detail and a richness of coloring, which call forth the 
admiration of the beholder. The principal belts near 
the equator have a reddish cast ; the hue is modified 



White clouds. 



Jupiter, Saturn, Uranus, and Neptime. 255 

from time to time, being sometimes salmon-colored and 
at others a rich rose pink. There are many subsidiary 
stripes of smaller size and less pronounced color. 

The whitish portions of the planet's disc are by no 
means devoid of interest. They look like aggregations 
of cumulus clouds, such as deck the summer sky. One 
who looks down from the top of a mountain upon a 
layer of clouds below may see the general aspect of the 
Jovian clouds. Small white, dark, and red spots are 
strewn here and there over the surface. 

In 1878 there suddenly appeared a pink spot of un- 
precedented dimensions ; the length is given as 30,000 re/spot 
miles, the breadth as 7,000. In another year its hue 
was a full Indian red. So completely did it dwarf all 
other recorded spots that it was henceforth known as 
the " great red spot." It faded away, and was almost 
invisible in 1883 and 1884. Since then it has had 
irregular spells of brightening, but has never recov- 
ered its pristine beauty. The time of rotation of the 
red spot is not the same as that of the adjacent cloud- 
forms. In 1890 a large spot was moving directly 
toward the red spot ; but it was diverted from its 
course, and passed by at one side of the spot. After it 
passed by it did not return to its original course, but 
remained at the higher latitude into which it had been 
shunted ; it passed the red spot at the rate of twenty 
miles an hour. Professor Keeler * has likened the 
great red spot to a sand bank in a river, past which the 
flecks of foam go scurrying. 

The red belts are thought to be cloudless regions ; Thered belts 
the sunlight striking against the whitish cloud-masses is 
reflected back in large measure ; but that which falls 
upon the red rifts between the clouds is not so well re- 

* Prof. James E. Keeler, of the Allegheny Observatory. 



2.S6 



A Study of the Sky. 



A red atmos- 
phere. 



fleeted. If Jupiter's atmosphere is red and the white 
masses are clouds floating in it at various heights, the 
general appearances are explained. What we have called 
the atmosphere may be a liquid having a reddish color. 
Not only do the different parts of Jupiter's cloud 
mantle rotate with different velocities, but even the 



Variable 
rotation. 




Fig. 120.— The Great Red Spot. 

great red spot has not kept a constant period of rota- 
tion. At first the whirling of the planet on its axis 



brought it around in 



9 hrs. 55 r 



34 s 



In 



seven years 



the period had lengthened seven seconds. If it had 
kept the new rate and Jupiter itself had been a solid 
rotating at the old rate, it would have gone clear around 



Jupiter, Saturn, Uranus, and Neptujie. 257 



the planet in less than six years. If Australia were cut 
loose from its moorings and drifted toward Africa, we 
should have a parallel to the drift of the red spot. 
During the past ten years (1886-96) the spot has ap- 
parently been at anchor. 

Though changes on Jupiter's face are not very rapid, 
no feature is permanent either in form or position. It is 
then a reasonable hypothesis that Jupiter has no solid 
crust. To this conclusion some other facts point. 
Though Jupiter is 1,300 times as large as the earth, it is 
only 316 times as heavy ; it is therefore only one fourth 
as dense and may plausibly be regarded as a fluid mass 
enveloped in a deep shell of cloud-laden vapor. 

But what is the cause of the abundant supply of 
clouds ? Why is not Jupiter's atmosphere clear like that 
of .Mars? Clouds cannot be formed unless there is 
heat to produce the vapors to which they owe their 
origin. As the sunlight is only one twenty-seventh as in- 
tense as ours, the necessary heat can hardly come from 
that source, and we are forced to conclude that Jupiter 
is itself a warm body. This conclusion is directly in line 
with the nebular theory, according to which all the 
planets were once heated bodies. Jupiter, being much 
larger than the other planets, would cool off more slowly 
and require a longer time to solidify. But if Jupiter be 
a hot body, why does it not shine with some such vivid- 
ness as a fixed star manifests ? A body may be hot 
without being luminous ; a kettle of boiling water would 
hardly fill the office of a student lamp. Jupiter may well 
be regarded as a semi-sun. Its interior may be a pasty 
mass of sufficient consistency to give considerable per- 
manence of location to such an object as the great red 
spot, which probably owes its origin to a disturbance in 
the depths of the planet. 



No permanent 
forms. 



Internal heat. 



A semi-sun. 



258 



A Study of the Sky. 



The moons. 



Discovery of 
the velocity 
of light. 



Rotation of 
the satellites. 



Jupiter is accompanied by a goodly retinue of attend- 
ants, five in number. Galileo discovered four of them, 
the smallest being of the size of our moon, while the 
largest is comparable with Mars. They are designated 
by Roman numerals, I being nearest to its primary and 
IV farthest away. As they circle round the planet, they 
are in occultation when hiding behind him, in eclipse 
when immersed in his shadow, and in transit when 
crossing his disk. The times of all these phenomena 
are given in the ' ' Nautical Almanac. 

Observations of them in the seventeenth century led 
to the discovery that light takes an appreciable time to 
fly from one world to another. How this came to pass 
is not difficult to understand. Let an astronomer observe 
the times of a number of eclipses of satellite I when 
Jupiter is in opposition, the earth at that time being at 
nearly the same distance from him for several weeks. 
Since eclipses occur at pretty regular intervals it will not 
be difficult for him to predict from his observations the 
times at which fresh eclipses will occur several weeks 
afterward. Meanwhile the earth and Jupiter are getting 
farther apart and the predicted eclipses come later than 
expected. The reason is that the light which brings 
from Jupiter the message that the eclipse has begun now 
takes longer to perform its journey than it did when the 
earth and Jupiter were nearer together. 

Spots have been seen on Jupiter's satellites at times ; 
attempts have been made to find their times of rotation 
by observing these. The moons have also appeared 
elongated. If one looks at an egg one hundred feet 
away, while it is held with its end toward him the egg 
appears round ; when it is held sidewise it looks oval. 
So the satellites, if really oval, will appear to be out of 
round at times. The high tides raised upon them by 



The fifth 



Jupiter, Saturn, Uranus, a?id Neptuiie. 259 

Jupiter may have elongated them. There is evidence 
that some of them, at least, keep the same face toward 
the planet. 

The fifth satellite, which was discovered by Barnard 
with the Lick telescope on September 9, 1892, is much satellite. 
smaller than the others, its diameter being estimated at 
one hundred miles. It is less than 70,000 miles from 
Jupiter's surface and occupies nearly twelve hours in 
making one revolution. Only the largest telescopes can 
deal successfully with it ; the other moons can be seen 
with a good opera-glass. People of extremely acute 
vision can see with the naked eye satellite III, which is 
660,000 miles from Jupiter's center, or IV, which is 
1,160,000 miles away, under favorable conditions. 

SATURN. 

The ancients regarded Saturn as the most distant of 
the planets because of his dimness and the slowness of f nd Gaii feof 
his motion. Little did they imagine that this dull-look- 
ing object would one day be transformed into a marvel 
which would ever after challenge the admiration and 
awaken the enthusiasm of mankind. Galileo was the 
first to perceive that it was no ordinary planet. So many 
imitators had followed in his footsteps, laying claim to 
greater discoveries than he had made, that he had grown 
wary. These men had seen twice as many moons 
circling around Jupiter as Galileo had announced. To 
baffle them he set forth his discovery about Saturn in 
the form of an anagram. This procedure had the de- 
sired effect, and the pseudo-scientists were put to flight 
by its uncanny array of disjointed Latin. The emperor 
Rudolph finally prevailed upon Galileo to arrange the 
letters of the anagram in their proper order ; it then 
became : "Altissimum planetam tergeminum obser- 



26o 



A Study of the Sky. 



The triple 
planet. 



The mockery. 



Galileo's 
affliction. 



Huyghens. 



The ball 
and ring. 



vavi " (The most distant planet three-fold I have ob- 
served). 

Galileo's imperfect telescope had shown Saturn as a 
large ball, flanked by two smaller ones. But in less 
than two years a change took place which was a sore 
trial to him. He says : 

Looking at Saturn within a few days I found it solitary, 
without the aid of its customary stars, and, in short, exactly 
round and well defined like Jupiter, and thus it still remains. 
Now what can be said of so strange a change ? Have the two 
lesser stars been consumed like spots on the sun ? Have they 
suddenly vanished and fled away ? Or has Saturn eaten up his 
children ? Or was the appearance a delusion and a snare, with 
which the glass has deceived me and many others who have 
often observed with me ? 

He never divined the cause of their disappearance. 
In his old age a veil was drawn over his eyes, which had 
done so much in unveiling the mysteries of the skies, 
and he wrote pathetically : 

Alas ! your dear friend and servant is entirely blind. Hence- 
forth this universe, which I have enlarged a thousand times be- 
yond the ideas of former ages, has shrunken for me into the 
narrow space which I myself fill in it. So it pleases God ; 
it shall therefore please me also. 

In less than fifty years after Galileo's anagram was 
given to the world, a Dutch astronomer, Huyghens by 
name, set another one afloat in the sea of scientific 
thought. His alphabetical agglomeration, when mar- 
shalled in correct array, took the following form : 
' ' Annulo cingitur, tenui, piano, nusquam cohserente, 
ad eclipticam inclinato " (It is girdled by a thin, flat 
ring, nowhere touching, inclined to the ecliptic). 

This admirably correct statement renders possible an 
explanation of the change which perplexed Galileo. 
To build up a mental picture of Saturn we must imagine 



262 



A Study of the Sky. 



Phases of 
the rings. 



Divisions of 
the ring. 



a rotating ball the polar axis of which is 70,000 miles 
long, while its equatorial diameter is 76,000 miles. 
Encircling this ball and lying in the plane of its equator 
is a thin flat ring, the outer diameter of which is 
173,000 miles, the inner diameter being 110,000 miles ; 
its thickness probably does not exceed 100 miles. 

As Saturn wheels about the sun in his appointed path 
we see the ring in different positions. Now it is turned 
edgewise to us, and is invisible because of its thinness. 
Again it is turned at such an angle that an imperfect 
telescope shows it as two projections, one on each side 
of the central ball. The greatest angle at which it is in- 
clined to our line of vision is 28 °. Saturn takes twenty- 
nine and one half years to perform one revolution about 
the sun, and the rings are edgewise to the sun twice 
during a revolution. Midway between these two times 
they are in the best position for observation. Two 
favorable years are 1899 and 19 14. The best views of 
Saturn in any particular year are obtainable when it is 
at opposition. Its mean distance from the sun being 
886,000,000 miles, it is then about 800,000,000 miles 
from us. 

Hitherto we have spoken of " the ring." It is really 
composed of three concentric rings lying in the same 
plane. The outermost ring is 10,000 miles in width, 
and is separated from the middle ring by a space 
2,200 miles wide, which is called "Cassini's division." 
Other fainter divisions have been glimpsed. The middle 
ring is 17,500 miles wide. These two rings are of the 
same yellow hue as the ball ; the innermost ring is very 
dark, and is known as the cr£pe ring, or gauze ring. It 
is 9,500 miles wide and there is no division between it 
and the ring outside of it ; between its inner edge and 
the ball is a space of 7,000 miles. 



Jupiter, Saturn, Uranus, and Neptune. 263 

As to the structure of the rings there has been much 
discussion ; they look solid, but mathematicians are not f 1 Jg U r ^J 1 ur s e of 
satisfied with appearances. The hypotheses of solidity 
and fluidity have both been rejected, because the rings 
would not be stable, but would be destroyed by precipi- 
tation upon the ball. Clerk Maxwell, the famous Eng- 
lish man of science, has shown that if the rings are 
composed of myriads of little bodies too small to be 
separately visible to us, the system is stable. So ele- 
gant and complete were Maxwell's researches, and so 
cogent was his train of reasoning, that the Cambridge 
students averred that he paid a visit to Saturn one 
evening, and cleared up the mystery with his own eyes. 

The largest telescopes have given no ocular proof of 
the correctness of Maxwell's theory ; that honor has Keeier's 

J \ spectroscopic 

been reserved for the spectroscope, which, in the hands observations, 
of Keeler, first gave a satisfactory demonstration. The 
work has since been confirmed by others. One of the 
offices of the spectroscope is to determine whether a 
body is approaching us or receding ; it is now possible 
to measure with a reasonable degree of accuracy the 
velocity of approach or recession. If Saturn's ring- 
system rotated as a solid mass the outer edge would 
move more swiftly than the inner one. If, on the other 
hand, the rings are composed of separate small bodies, 
those bodies which are near the inner edge must travel 
more rapidly than those near the outer edge, because 
they are more strongly attracted by the ball. Dr. 
Keeier's beautiful photographs of the spectrum of the 
ring-system show not only that the outer edge moves 
more slowly than the inner one, but that the inter- 
mediate portions move with intermediate velocities ; 
these velocities agree with what would be expected of 
bodies moving in conformity with Kepler's laws. 



264 A Study of the Sky. 

Thus another instance is added to the list of cases 
where mathematicians, emboldened by confidence in 
the unerring symbols and apparently immutable laws 
with which they deal, have described processes going on 
in distant worlds, which observers have afterward veri- 
fied. 

Is the system of rings really stable ? What must be 
Ar bi th ? e rings continually happening in a dense swarm of bodies mov- 
ing with various velocities ? Are not collisions frequent ? 
When two of them collide, the swifter is checked, and 
the slower accelerated. If the earth's motion about the 
sun were suddenly checked, it would seek a new path of 
smaller diameter. If its velocity were increased by a 
blow from some body which was chasing it, the earth 
would swing out into a larger orbit. Collisions in 
Saturn's ring must therefore cause a broadening of the 
ring, since some of the bodies are getting larger veloci- 
ties and others smaller ones. 

The earliest drawings show a much wider space be- 
tween the ball and the ring than now exists, and thus 
bolster up the theory, but, on the other hand, careful 
measures of the dimensions of the ring system, made 
during the past fifty years, afford no evidence of enlarge- 
ment. 

The dark inner ring is called the gauze ring, because 
it is not opaque ; through its edge one can sometimes 
see the ball. Professor Barnard has made an interesting 
observation with reference to its transparency. One of 
Saturn's moons, which had been eclipsed in the shadow 
of the ball, emerged into the sunlight for a while, and 
then plunged into the shadow of the dark ring. It did 
not disappear at once, but grew fainter till it en- 
countered the shadow of the inner bright ring, then it 
vanished. The gradual diminution of its brightness 



The gauze ring. 



The ball. 



Jupiter, Saturn, Uranus, and Neptune. 265 

indicates that the dark ring is denser on its outer edge 
than on its inner. It is likely that the small bodies are 
more closely crowded together near one edge than at 
the other. 

The ball, though large, is not heavy ; its average 
density is only one eighth that of the earth, being con- 
siderably less than that of water. The equator is brighter 
than the regions on each side, and faint belts are some- 
times seen well up toward the poles. There is but little 
change in appearance from year to year. In December, 
1876, a small white spot suddenly burst forth near the 
equator, and was visible for a month ; the planet's rota- 
tion carried the spot around in 10 hrs - i4 min - The placid 
cloud-mantle in which the ball is enveloped hides most 
of the commotion within ; the interior does not seem to 
be in such a state of activity as Jupiter manifests. 

Eight satellites accompany Saturn. Their names, 
from the outermost inward, are : Iapetus, Hyperion, 
Titan, Rhea, Dione, Tethys, Enceladus, and Mimas. 
Titan, the largest, is four times as big as our moon, and 
occupies nearly sixteen days in a revolution. The exist- 
ence of Cassini's division in the rings has been attrib- 
uted to Titan's pull, which so disturbed the moonlets 
which once were there that they forsook their paths. 
Iapetus is 2,225,000 miles from the planet's center, and 
looks twice as bright when it is on one side of it as when 
on the other side. This is explained by the hypothesis 
that a large part of the surface is much darker than the 
rest, and that, like our moon, it keeps the same face to- 
ward its primary. 

URANUS. 

Uranus was discovered by Sir William Herschel. This 
remarkable man, to whom astronomy owes so much, Herschel - 
was a native of Hanover. His father was a musician, 



The moons. 



Sir Willis 



266 



A Study of the Sky. 



A musician. 



He grinds 
mirrors. 



and the son was diligently instructed in that art. At the 
age of seventeen he was oboist in a regiment of Hano- 
verian guards ; but two years afterward he deserted, and 
employed his musical talents in other directions. He 
speedily rose to prominence, and in a few years became 
organist of the Octagon Chapel at Bath. The society to 
which he was thus introduced was brilliant and fashion- 
able, and his talents brought him prominence and pros- 
perity. But despite manifold professional engagements, 
which would have entirely absorbed the energies of an 

ordinary man, 
his restless mind 
reached out into 
other fields. Studies 
in Italian, Greek, 
pure mathematics, 
optics, and astron- 
omy failed to satiate 
his thirst for knowl- 
edge. 

When thirty-five 
years of age he ob- 
tained the use of a 
small telescope. Its 
revelations fired him 
with a purpose to 
obtain a knowledge 
of the construction of the heavens. He set himself reso- 
lutely at the task of making a larger telescope. His 
pertinacity knew no limit. Mirror after mirror was 
ground and polished. His sister Caroline, who was his 
constant attendant, writes: "My time was taken up 
with copying music and practicing, besides attendance 
upon my brother when polishing, since by way of keep- 




Fig. 122. — Sir William Herschel. 



Jupiter, Saturn, Uranus, and Neptune. 267 

ing him alive I was constantly obliged to feed him by 
putting the victuals by bits into his mouth." By day 
he ground mirrors and gave music lessons ; in the even- 
ings he conducted concerts and oratorios, running out 
at intervals to look through a telescope ; at night he 
scanned the sky. 

After seven years spent in this way Uranus swam into Uranus swims 
his ken on March 13, 178 1. He tells of the discovery into his ken. 
thus : ' ' On this night, in examining the small stars 
near Eta Geminorum I perceived one visibly larger 
than the rest. Struck with its uncommon appearance 
I compared it with Eta Geminorum and another star, 
and finding it so much larger than either, I suspected it 
to be a comet." Professional astronomers began to 
observe the new body, and later computations showed 
that its orbit was nearly a circle ; it was therefore no 
comet, but a new planet. 

The discovery aroused great enthusiasm, since all the 
other planets had been known from the earliest an- prosperity, 
tiquity. Herschel was at once brought into royal favor, 
received a pension, and was given all needed funds for 
constructing a twenty-foot reflecting telescope, which 
was much larger than any hitherto made. With this 
instrument and a forty-foot, built afterward, Herschel 
carried forward the wonderful series of observations 
which made him supreme among astronomical observers 
of all ages. His faithful sister Caroline was his indefati- 
gable assistant, recording his observations at night, as 
he dictated them to her, and making tedious calculations 
by day. Herschel and Uranus were discovered sim- 
ultaneously ; the importance of the discovery of the 
man is a sufficient excuse for devoting so much atten- 
tion to him. 

Of Uranus little is known which cannot be expressed 



268 



A Study of the Sky. 



Details about 
Uranus. 



Short and 
simple annals. 



Its discovery. 



in cold figures. Its distance from the sun is 1,780,000,- 
000 miles, and its diameter is 32,000 miles. Its time of 
revolution is eighty-four years. It is visible to the 
naked eye, and even the most powerful telescopes show 
simply a greenish disc on which there are faint belts. A 
dense atmosphere produces marked absorption bands in 
its spectrum. What is beneath the atmosphere no one 
can tell. Four satellites attend it ; strange to say, the 
plane in which their orbits lie is so tipped up as to be 
nearly perpendicular to the plane of the planet's orbit. 
The moons also revolve from east to west, while all 
other satellites heretofore considered go from west to 
east. 

NEPTUNE. 

More than 1,000,000,000 miles beyond Uranus plods 
slow-footed Neptune, the outpost of the solar system. 
Its mean distance from the sun is 2,792,000,000 miles, 
and its diameter is 35,000 miles. An opera-glass will 
render it visible ; it exhibits in a large instrument a 
small greenish disc on which no details can be seen. 
Like Uranus it is enveloped in a dense atmosphere, 
through which struggles sunlight only giro- as intense as 
ours. Its one moon is a tiny speck of light, and is 
supposed to be about as big as ours. Like the moons 
of Uranus it revolves backward in its orbit. Neptune 
requires 165 years to complete a journey around the 
sun. 

The circumstances of its discovery are of high interest 
and involve one of the greatest triumphs of mathemati- 
cians. The discovery arose from the strange behavior 
of Uranus, which refused to follow the path which had 
been laid down for it by the mathematicians. After they 
had thought that it was securely ensnared it persisted in 
breaking the chains of their analysis, wandering into 



problem. 



Jupiter, Saturn, Uranus, and Neptune. 269 

by and forbidden paths. Sixty years after its discovery 

it had gone so far astray that no one could doubt that 

something was wrong ; to be sure, the theoretical and 

the actual planet were so close together that the unaided 

eye would see them as one body, but the discrepancy An intolerable 

was intolerable to a mathematical mind. 

So firmly convinced were astronomers of the accuracy 
and universality of Newton's law of gravitation that 
they became convinced that the observed irregularities 
must be due to the attraction of some other body, which 
pulled Uranus away from its proper path. It is a prob- 
lem of no mean difficulty to compute the effect of one 
planet's pull on another, when the masses and relative 
positions of the bodies are known. How much a difficult 
greater the difficulty of discovering the mass and success- 
ive positions during a series of years of an unknown 
body, which, as the upshot showed, was more than 
1,000,000,000 miles away from Uranus. Several eager 
minds attacked the problem, but found it too difficult 
for their powers. 

Mr. J. C. Adams, a student of the University of Cam- 
bridge, resolved to look into the matter as soon as his 
final examinations were over. In January, 1843, having 
graduated as senior wrangler, he set to work. In Octo- 
ber, 1845, he communicated his results to the astrono- 
mer royal, who naturally thought it very improbable that 
a young and unknown student should have solved so 
profound a problem. He looked over the papers, and 
seeing that they gave evidence of careful research, 
wrote to their author concerning an obscure point in the 
investigation. Unfortunately Mr. Adams did not reply 
at once, and his communication was pigeon-holed. 

Meanwhile a young Frenchman, Leverrier, had con- 
centrated his marvelous powers upon the problem. In 



Adams. 



Leverrier 
calculates. 



270 



A Study of the Sky. 



Challis hunts. 



Galle finds it. 



November, 1845, he sent a paper to the French Acad- 
emy, in which he showed that no known causes of error 
would account for the wanderings of Uranus. A second 
paper in June of the next year assigned to the disturbing 
body a definite place in the zodiac. When this news 
reached England the astronomer royal was astonished to 
find that Adams and Leverrier were in substantial 
agreement. 

He at once wrote to Professor Challis of Cambridge, 
asking him to search for the suspected planet. Professor 
Challis was not very enthusiastic, but set about the work 
with due regard to thoroughness and to leisurely dignity. 
He began to take the positions of all visible stars in the 
suspected region, going over the same locality three 
times. It was his intention at some convenient season 
to prepare a map from each night's work, and by com- 
paring them to find out if any one of the objects noted 
had moved. 

While he was engaged in manipulating his astronomi- 
cal drag-net, Leverrier, w T ho knew nothing of the work 
of the Englishmen, completed his investigations and re- 
quested Galle, director of the observatory at Berlin, who 
was already in possesssion of an excellent star chart, to 
look in a certain place ; there he would find the planet. 
The letter was received on September 23, and on the 
same night Galle came upon the planet within a degree 
of the predicted place. When the news reached Eng- 
land Professor Challis bestirred himself, looked over his 
note-books, and found that he had observed the planet 
on August 4 and August 12. Had he been prompt in 
comparing his results, he would have detected the new 
body before Galle looked for it ; but his burst of speed 
came after the race was over. Thus did confidence and 
energy win the victory over doubt and delay. 



CHAPTER XVI. 

COMETS AND METEORS. 

" Stranger of Heaven, I bid thee hail ! 
Shred from the pall of glory riven, 
That flashest in celestial gale — 

Broad pennon of the King of Heaven." 

—Hogg. 

"And certain stars shot madly from their spheres, 
To hear the sea-maid's music." 

— Shakespeare. 

Few astronomers devote themselves to searching for 
comets ; such work requires extreme patience, involves 
irregular hours of work, requires very little mathemati- 
cal training, and is quite monotonous except at the su- 
preme moment of discovery. If the moon is bright in 
the early evening the comet hunter waits till it has set. 
Night after night he shifts the pointer on his alarm clock 
and alters his hours for sleep. When once at his tele- 
scope he sweeps over a certain part of the sky, keeping 
his eye closely confined at the eyepiece, that nothing 
may escape. If a faint wisp of nebulous light comes 
into view he inspects it with care ; if he does not recog- 
nize it he looks in his catalogue of nebulae to see if it is 
described there. If not, he concludes that it is new, and 
watches it for an hour or so to see whether it appears to 
move among the surrounding stars. Any motion be- 
trays its cometary nature ; if it remains at rest it is a 
nebula. A comet may also be discovered by an astro- 
nomical photographer, who finds its image impressed 
upon one of his plates. 



Comet hunting. 



272 



A Study of the Sky. 



The comet 
ensnared. 



Three obser- 
vations. 



The new comet is promptly announced, so that obser- 
vations of it may begin at once. Its right ascension and 
declination are measured by comparing it with known 
stars which lie along its path. The star catalogues con- 
tain the places of several hundred thousand stars, so 
that a known one can always be found in the vicinity of 

the comet. With 
his micrometer, 
which has been 
previously de- 
scribed, the as- 
tronomer meas- 
ures the position 
of the comet with 
reference to the 
star. He may 
rind, for instance, 
that the comet's 
right ascension is 
29.42 sec - greater 
than that of the 
star, and the dec- 
lination is 4' 
13". 2 less. Ap- 
plying these 

Fig. 123. — Discovery of a Comet by Photography. Quantities tO the 

known right ascension and declination of the star he ob- 
tains the comet's place. After a comet's place has been 
measured three times, a preliminary orbit of it is com- 
puted and its location is predicted for a month or so in 
advance, so that observers may more readily keep on 
its track. When a large number of observations have 
been made, a more accurate computation of its path is 
executed. 




Comets and Meteors. 



273 



Its orbit must be a parabola, or an ellipse, or an hy- 
perbola ; so Newton's law demands. Most comets move 
in orbits so nearly parabolic that it is customary to com- 
pute the first orbit on the assumption that it is a parab- 
ola. If the comet refuses to follow this curve, it is 
generally found to move in an ellipse. Hyperbolic paths 
are rare. While an ellipse is a closed curve, a parabola 
or an hyperbola is not. 

Some elementary notions 
about celestial mechanics as- 
sist one in understanding the 
history of these wanderers, 
prior to their introduction to 
us. If one of them is mov- 
ing slowly along in space, 
millions of millions of miles 
from the sun, the attraction 
of the latter compels it to fall 
toward him. Were the sun 
and comet originally at rest, 
the comet would make 
straight for the sun ; but as 
both are moving, the comet FlG - ^.-paths of Comets. 
comes down in a parabolic curve, whisks around the 
sun, and is off again, never to return. 

If the comet, while passing through the solar system, 
happens to come near one of the larger planets, its path 
may be seriously altered. If Jupiter, for example, is so 
situated with reference to the comet that its attraction in- 
creases the latter' s velocity, the orbit will become an 
hyperbola. But if Jupiter diminishes the stranger's ve- 
locity, the orbit changes to an ellipse, and the comet is 
compelled to become an attache of the sun. Jupiter's 
brigandage has led to the capture of several small com- 



The shape of 
the orbit. 




A planet's 
attraction. 



274 



A Study of the Sky. 



Groups of 

comets. 



The make-up 
of a comet. 



Light and airy. 



ets, which are denominated his family. Saturn, Uranus, 
and Neptune have also indulged, to a lesser extent, in this 
piratical business. 

There are a few instances of groups of comets which 
have nearly the same paths during their visibility, but 
revolve in different times. The comets of 1668, 1843, 
1880, 1882, and 1887 form such a group. Each of them 
passes close to the sun's surface, and is therefore ex- 
posed to a tremendous heat, and also subjected to a power- 
ful tidal strain. A modern French mathematician has 
proved that if a comet be disrupted in this manner, its 
fragments will afterward pursue similar paths. 

Comets are erratic, not only in their motions, but also 
in their appearances ; they are continually doing some- 
thing outre. The peculiarities of their behavior must 
be attributed largely to their make-up. They are not 
compact masses of matter like the earth or the moon, but 
rather loose aggregations of small bodies, which fly 
along together like so many grape-shot. These bodies 
must sometimes be reduced to liquids, when exposed to 
intense solar heat, and carry with them a certain amount 
of gaseous matter. Of their sizes no certain estimate 
can be made, but they probably vary from the merest 
particles, like grains of sand, to more substantial masses 
as big as a house, or even larger. The connection be- 
tween certain comets and meteoric swarms renders it 
almost certain that comets are largely bunches of small 
bodies. 

Large as comets are, they are comparatively insignifi- 
cant in mass and density. As they dash along over the 
face of the sky they scarcely obscure even the faintest of 
the stars which lie behind them. Though their texture 
is so diaphanous, yet the gases which accompany the 
more solid portions are sometimes of sufficient refract- 



Comets and Meteors. 275 

ive power to bend by a minute amount the rays of light 
coming through them from the stars beyond. Were 
comets as dense as planets, some of them would derange 
the orbits of the planets seriously by their attraction. 
It has been estimated that 100,000 of the largest comets 
put together would not weigh as much as the earth. 

Having premised these facts we are better able to changesof 
understand the changes which take place in a comet's a PP earan ce. 
appearance as it approaches the sun and recedes from 
him again. As it draws near, the increasing heat and 
the electrical influences which the sun probably exer- 
cises cause it to brighten. The densest portion of 
the cometary mass, which is called the nucleus, comes 
into prominence as a hazy mass, more compact and 
brilliant than the surrounding nebulosity. 

The tail forms gradually, and prudently keeps on the 
side away from the sun. The nucleus seems to be the 
seat of the greatest activity ; it spurts out jets toward 
the sun, or throws off masses of vapor, which are driven 
back into the tail. The entire body of the comet is 
affected to an extent which would be impossible were it 
a single compact mass. After the comet has passed 
perihelion the disturbances die away ; the nucleus grows 
fainter and more sluggish in its actions ; the tail shortens 
up and disappears. After a few weeks or months only 
a pale nebular gleam remains, which soon vanishes. 
Such is a crude outline of the general behavior of a 
comet of moderate size and average friskiness. 

We proceed to consider various details. First as to 
the jets and envelopes. These are rarely seen in faint envelopes. 
comets, but are conspicuous in bright ones. The sun- 
ward side of the nucleus is the seat of forces which 
project bright jets ; as the jets rise higher and higher 
they spread out and become lost in the general nebu- 



The tail forms. 



2 7 6 



A Study of the Sky. 



Umbrella-like 
forms. 



The tail. 



losity of the comet's head. The formation of envelopes 
a less violent and more orderly procedure. These 



15 



umbrella-shaped forms rise toward the sun one after 
another at intervals of some hours, as if the comet 
were endeavoring to protect itself from the solar radia- 
tion. As they ascend they expand and grow fainter till 
their distinctive appearance is lost, like that of the jets. 
The magnificent trains which accompany bright 




Fig. 125. — Jets and Envelopes. 

comets are their most characteristic features. Often 
they are tens or even hundreds of millions of miles 
in length. Occasionally they are nearly straight, but 
usually they have the graceful contour of the plume on 
a knight's crest. The material projected toward the 
sun by the jets and envelopes encounters a resistance 
which destroys its original motion, and drives it back- 
ward past the nucleus into the tail. If a locomotive 
puffed its smoke forward instead of upward, it would be 
swept backward in much the same fashion. 



Comets and Meteors. 277 

The repellent force, which triumphs so signally over 
the pull of the sun on these little solid, liquid, and ^ c e g rical 
gaseous emanations, is supposed to be electrical. In 
any physical laboratory may be seen pith-balls and 
light strips of paper, which are lifted by electrical forces 
in opposition to the force of gravity. In a similar way 
the lightest portions of a comet may be driven off by an 
electrical repulsion originating in the sun, while the 
heavier portions are dominated by his attraction. 

The spectroscope certifies to the presence of a few 
known elements in comets. The predominant gases Different 

1 ° materials. 

seem to be hydro-carbons, which are compounds of 
hydrogen and carbon. Sodium and iron have been 
certainly identified, and magnesium and calcium are 
thought to be present. What happens to these differ- 
ent materials as they are being driven off by the 
electrical repulsion ? Manifestly the lightest elements 
attain the greatest velocity ; moderately heavy ones 
move with less velocity, and the heaviest with still less. 
These motions, combined with the orbital motions of 
comets, cause various degrees of curvature in their tails. 

There are three special types of tails. Tails of the first 
type are nearly straight and point almost directly away T yP es of taiIs - 
from the sun. They are believed to be composed largely 
of hydrogen. The majority of the trains belong to the 
second type, and are gracefully curved ; here the repul- 
sive force has less effect than before, as the particles on 
which it acts are heavier. Tails of this type are com- 
posed of hydro-carbons. The third type of tail is un- 
common ; it, too, is plume-like, but it curves very 
sharply at the comet's head, and trails behind the nu- 
cleus as the latter moves swiftly in its appointed path. 
Iron vapor is thought to be present in such tails. 

The appearances of the three types are aptly repre- 



2 7 8 



A Study of the Sky 



The smoke of 
a locomotive. 



Anomalous 
tails. 



Fate of comets. 



Companions. 



sented by the smoke which issues from a freight engine 
moving in a quiet atmosphere at a moderate speed. If 
the steam pressure is very high, the puffs of smoke go 
nearly straight up ; if the pressure is only moderate, the 
stream of smoke forms a curving plume ; when the 
steam is nearly shut off the smoke trails lazily behind the 
smoke-stack. 

Some comets exhibit more than one type of tail ; even 
so strange a phenomenon as a tail pointing directly to- 
ward the sun has been observed. Wonderful changes 
have been noticed, as in the case of Swift's bright comet 
of 1892. On April 4 its tail was straight and twenty 
degrees in length, but consisted of two distinct branches 
lying close together. On the next night a third tail was 
seen between the other two ; each of the three appeared 
to be composed of several, so that the whole looked like 
a fan partially opened. Within twenty-four hours more 
one tail vanished, and the other two joined their bound- 
aries. One of these then grew bright at the expense of 
the other, and finally split up into half a dozen branches. 
These are the most noteworthy of the changes which 
took place in five days. 

The particles which are driven off into the tails are 
lost. A periodic comet, i. e., one which moves in an 
ellipse and returns at stated intervals, loses some of its 
substance at each perihelion passage, and must be 
wasted away in time. 

Comets are sometimes accompanied by smaller com- 
panions. In 1889 one was seen which had no less than 
four of these attendants ; two of them were very faint, 
and did not last long ; for a while the other two were 
veritable twins, and bore a striking resemblance to the 
main comet. Like foolish children they cut the maternal 
apron strings and began to move away ; this move sealed 



28o 



A Study of the Sky 



Changes of 
brightness. 



Superstitious 
terror. 



Collisions. 



the fate of one of them, which soon faded into invisibil- 
ity. The other made a brave show for a time, but came 
back in a few weeks with a swelled head and no tail. 
The moral is obvious. 

Though the brightness of a comet generally changes 
with considerable regularity as its distances from the sun 
and earth vary, there are often anomalous variations, 
which are best explained by electrical discharges between 
the small masses of which it is made up. The existence 
of such discharges is not merely conjectured. During 
the past few years spectroscopic observations of comets 
have gone hand in hand with laboratory experiments 
upon gases confined in Geissler tubes, and lit up by elec- 
tric discharges. A mass of evidence has thus been ac- 
cumulated which cannot be set aside ; unfortunately it 
is too technical to be reproduced here.* Suffice it to say 
that the coincidences between electrical appearances pro- 
duced in the laboratory and those observed in the spec- 
tra of comets are very complete. 

It is well known that in past centuries comets were 
objects of superstitious terror, not only to the ignorant, 
but even to the higher classes of society. The comet of 
1528 is thus described by Ambrose Pare : 

This comet was so horrible, so frightful, and it produced 
such great terror in the vulgar that some died of fear and others 
fell sick. It appeared to be of excessive length, and was of the 
color of blood. At the summit of it was seen the figure of a 
bent arm, holding in its hand a great sword, as if about to 
strike. At the end of the point there were three stars. On 
both sides of the rays of this comet were seen a great number 
of axes, knives, blood-colored swords, among which were a 
great number of hideous human faces, with beards and brist- 
ling hair. 

Though some unaccountable superstitions still survive 

* See Scheiner's " Astronomical Spectroscopy," pages 207-22. 



Comets and Meteors. 281 

among fairly educated members of enlightened com- 
munities, very few of them are connected with, com- 
ets. But there is apprehension in many quarters con- 
cerning the results of a collision between a comet and 
the earth. The fear is that the great heat generated by 
the impact would blast the earth's surface as effectually 
as if it were tossed into a gigantic furnace, and would 
dissolve all its inhabitants in the twinkling of an eye. It No 
appears from what we have learned of the constitution of dan ser. 
comets that nothing of the sort is to be feared. Astron- 
omers would be delighted if any ordinary comet should 
run into the earth, for there would be a shower of fall- 
ing stars most beautiful to behold. A very large comet 
might make more trouble ; for such an one probably con- 
tains a good supply of metallic masses, which would come 
through the air without being consumed. Fortunately 
they would not be close together, for stars have been 
seen shining with undiminished splendor through the 
nuclei of large comets ; a city as large as Chicago might 
catch only a few of the celestial missiles. Some of them 
might be as large as houses and cause decided havoc 
where they struck. The celestial spaces are so vast in 
comparison with the bodies which traverse them that 
there is little danger to be apprehended from comets. 

In November, 1892, there was a comet scare, caused 
by the apprehension that Biela's comet* was about to 
dash against our planet. The fright inspired in certain 
localities is evidenced by the following press-dispatch 
from Atlanta, Georgia : 

The fear which took possession of many citizens has not yet 
abated. The general expectation hereabouts was that the 
comet would be heard from on Saturday night. As one result 
the confessionals of the two Catholic churches were crowded 



A comet scare. 



Holmes's faint comet was erroneously thought to be a return of Biela's. 



282 



A Study of the Sky 



The stifling air. 



Fine comets. 



yesterday evening. As the night advanced there were many 

who insisted that they could detect a change in the atmosphere. 

The air, they said, was stifling. It was wonderful to see how 

many persons gath- 
ered from different 
sections of the city 
around the news- 
paper offices, with 
substantially the same 
statement. As a 
consequence many 
families of the better 
class kept watch all 
night, in order that 
if the worst came they 
might be awake to 
meet it. The orgies 
around the colored 
churches would be 
laughable, were it not 
for the seriousness 
with which the wor- 
shipers take the mat- 
ter. To-night (Sat- 
urday) they are all 
full, and sermons 
suited to the terrible 
occasion are being de- 
livered. 

So great is the 
number of splendid 
comets the histories 
of which are written 
in astronomical an- 
nals, that it would 
be a hopeless task 

to enumerate the thousands of interesting details about 

them. We pay brief attention to a few. 

The great comet which appeared in September, 1882, 




Fig. 127. — Holmes's Comet. 



Comets and Meteors. 283 

was the most magnificent one of recent years. It was 
bright enough to be visible in full daylight, close to o f h jgg° met 
the sun. On September 17 it passed across the sun, 
coming within 300,000 miles of the photosphere. 
Though it thus dashed directly through the corona, 
and may indeed have encountered some of the solar 
prominences, its speed was unabated. But the intense 
heat to which it was exposed, together with the strain 
caused by the tidal action of the sun, apparently dis- 
rupted the nucleus. In less than a month it exhibited 
two centers of condensation. As the days rolled by still 
further changes took place, until the nucleus had be- 
come 50,000 miles long, and was ornamented by a 
number of centers of condensation, the largest of which 
was 5,000 miles in diameter. 

The tail, at its best, was 100,000,000 miles in length, 
and stretched across the sky as a splendid golden bar. 
Along its track were scattered filmy debris, in the form 
of companion comets six or more in number. For 
nearly two months there projected in front of its head a 
luminous sheath, as though the comet were a sword 
which was being thrust into its scabbard. 

The spectrum was very bright, and indicated the 
presence of hydro-carbons, sodium, and iron ; calcium 
and manganese were also suspected. The comet was 
not lost to view till it had reached a distance of nearly 
500,000,000 miles from the sun. Its orbit is a very 
elongated ellipse, and it is expected to return in the 
middle of the twenty-seventh century. 

Encke's comet was discovered in 1786, and was found Encke - S comet 
to be making its round trip in only three years and a 
quarter, the shortest known cometic period of revolution. 
It is insignificant in appearance, but made trouble for 
astronomers as soon as they had obtained a fair grip 



Filmy debris. 



284 



A Study of the Sky. 



Biela's comet. 



Twins. 



A meteoric 
shower. 



on it. No matter how carefully they predicted its 
successive returns, it always outran the figures, and 
arrived at perihelion ahead of time. Such an effect 
would be produced by encounter with meteoric bodies, 
which offered a resistance to its motion. For a body 
which is retarded loses " centrifugal force," and is con- 
sequently pulled nearer to the sun, and compelled. to 
describe a smaller orbit, in which it goes more rapidly 
than before. Should the resistance continue, Encke's 
comet must inevitably be drawn into the fiery embrace 
of the sun. 

Biela's comet was discovered in 1826, and was soon 
proven to be one of short period ; it should come 
around once in six and three fourths years. In 1832 
this harmless object gave rise to a comet-scare ; for the 
fact became noised abroad that it crossed the path of the 
earth, and people jumped to the conclusion that there 
would be a collision. But when the comet crossed the 
earth' s orbit our planet was many millions of miles away. 

Thirteen years afterward the comet split in twain, 
under the very eyes of the watchers. The operation 
occupied several days, and after the parts had separated 
to a distance of nearly 150,000 miles, tails were shot 
out, and nuclei blazed up in rivalry. The original 
comet had possessed neither of these marks of cometic 
blue blood. They interchanged cometary compliments 
by alternately brightening and fading out. In 1852 
they were seen again, the distance between them being 
then ten times as great as before. They were still ex- 
changing compliments, and thus politely bowed them- 
selves out ; for they have never been seen since. 

On November 27, 1872, the earth, when crossing the 
orbit of the missing comet, encountered a fine meteoric 
shower. The comet should have been millions of miles 




Fig. 128.— Photograph of Rordame's Comet, showing Masses of Matter Driven 

Off into the Tail. 

The motion of the comet causes the stars to appear as streaks on the negative. 



286 



A Study of the Sky. 



Lexell's comet. 



Supposed 
returns. 



beyond on that date. Perhaps the earth did not dash 
into the comet, but into a mass of meteoric matter 
which was following in its wake. In 1885 there was 
another shower, and again in 1892 ; these were proba- 
bly due to the same group of bodies. Either the comet 
has become invisible, or has met with some accident, 
which has disintegrated it. 

Lexell's comet is perhaps the most tantalizing one 
with which astronomers have had to deal. It was first 
seen in 1770, and Lexell found that it was moving in an 
elliptical orbit, with a period of five and one half years. 
It did not reappear in 1776, but the earth was not then 
in a favorable position with reference to it and the sun. 
In 1 78 1 circumstances were favorable, but the comet 
was a truant. Lexell and Laplace investigated the 
matter, and detected Jupiter in the role of mischief- 
maker. Before 1767 the comet had come so near this 
planet that its previous orbit had been transformed in 
the five and a half years ellipse. In 1779 it came 
altogether too near to Jupiter, and was tangled up 
among his moons ; the moons moved on with their 
accustomed serenity, but the comet's orbit was so 
altered that it was given up for lost. But in 1843 a 
comet appeared whose orbit was somewhat similar to 
that of the long-lost Lexell. Leverrier went to the 
bottom of the question, and decided against their iden- 
tity. 

In 1889 Mr. W. R. Brooks* found a comet which has 
already been mentioned as accompanied by four com- 
panions. It too had been troubled by Jupiter, and had 
skirmished with his moons. Surely this was the re- 
turned prodigal ; but months of tedious calculation ren- 
dered its identity with Lexell's doubtful. Six more 

* Of Geneva, N. Y. : director of the Smith Observatory. 



Comets and Meteors. 



287 



years rolled by, and in August, 1895, Dr. Swift* picked 
up a comet which proved to be a claimant for Lexell's 
vacant chair. A European astronomer has made what a crucial test, 
he considers to be a crucial test of the matter, and an- 
nounces that Lexell is found at last. 




Fig. 129.— Comet c, 1893 (Brooks). 

The designation of this comet indicates that it was the 

i«i i' 1 • <-r>i r 1- Comet c, 1893 

third one discovered in 1893. The first one discovered (Brooks). 
in a given year is called comet a, the second comet b, 
etc. When this comet was first seen it had two tails. 
The main tail was beautifully symmetrical. Four years 

* Director of the Lowe Observatory, Echo Mountain, Cal. 



288 A Study of the Sky. 

afterward its beauty was gone. It was bent and 
shattered. The subsidiary tail was no more, and the 
principal tail was full of knotty masses of nebulosity. 
The appearance suggested that the comet had en- 
countered some resisting medium, which had struck its 
tail near the middle, and bent it. The comet itself was 
considerably brighter. The strange appearance of the 
tail may have been due to some other cause, for comets 
are noted for trickiness. 

SHOOTING STARS. 

Space not We are accustomed to think of space as empty, ex- 

empty. . 

cept where here and there a massive sun, or an obedient 

planet, or perchance an erratic comet pursues its lonely 
way. But the case is far otherwise. Innumerable 
small bodies traverse that part of space in which the 
solar system is now, in every direction. They are dark 
and cold. Those in our neighborhood are revolving 
about the sun, which is as careful to enforce obedience 
upon these specks of matter as upon the planets them- 
selves ; each has its own curve, and obeys the law of 
gravitation. 
The air is a When one of them collides with the earth a shooting 

star is produced. The shooting star does not strike the 
earth's surface, but impinges upon its atmosphere. So 
swift is its motion that it flames into incandescence 
when it encounters the higher strata of the air, just 
as a cannon ball is heated when it strikes a target. 
If the shooting star is coming directly toward the ob- 
server, so that he looks endwise at its path, it is simply 
a bright spot which flashes out for an instant. The vast 
majority of meteors dart at one side of the observer, and 
traverse long paths across the heavens. One can hardly 
look at the sky for fifteen minutes, on a clear moon- 



target. 



Comets and Meteors. 289 

less night, without seeing at least one of these bodies. 
If two men in neighboring towns watch meteors ior an 

, 111 1 Observations 

hour or two, and each marks on a star map the apparent for distance. 
path of every one which he sees, noting also the time at 
which he observes it, the height of any meteor which 
both have observed may be calculated. For the ap- 
parent path as seen by one man is slightly different from 
that seen by the other, and if the distance between the 
observers is known, the distances of the meteor from 
each of them at the instants of its appearance and disap- 
pearance can be found by a simple calculation. In this 
way the average height of a shooting star has been 
found to be seventy-five miles when it is first seen, and 
fifty miles when it disappears. Their visible paths are 
forty or fifty miles long ; their average velocity is 
twenty-five miles per second. 

Estimates of their sizes and weights are obtained from 
the amount of light which they emit. One which rivals meteors 
Venus at its best may weigh from fifty to one hundred 
grains. Faint ones weigh less than a grain ; many of 
them may be likened to grains of sand or canary seeds. 
One observer sees only a very small fraction of the total 
number which bombard the earth daily ; he can ordi- 
narily see from four to eight an hour. If a sufficient 
number of observers were distributed uniformly over the 
entire earth they would see from one to two millions 
every two hours. 

When a great meteoric shower comes, the sky is 
veined with thousands of luminous paths; all of them The radiant, 
prolonged backward meet in a certain place, which is 
called the radiant. It must not be supposed that the 
meteors emanate from this point, and diverge as they 
come on. The little bodies, which have joined in so 
bootless a fusillade against the earth, are really traveling 



290 



A Study of the Sky. 



Definite times 
for showers. 



in parallel paths, like the drops in a rain storm. One 
who looks out of the rear door of a passenger train 
notices that the rails appear to converge in the distance. 
In the same manner the parallel meteoric paths seem to 
converge to the distant radiant. If the radiant of a 
shower is in the constellation Andromeda, the meteors 
are called Andromedes ; if in Perseus, Perseids, etc. 

One bright shower is expected within a day or two of 
November 13 each year. The reason for this will ap- 
pear from a simple illustration. Suppose that a man 
walks round and round a circular grass plot upon which 
a spray of water is being thrown from without. Just as 



( ( 




j 1 



A meteoric 
river. 



The August 
meteors. 



Fig. 130.— A Besprinkling. 

often as he passes the spot where the stream of water 
plays he is besprinkled. Replace the man by the earth, 
and the stream of water by a mighty river of meteoric 
matter, which persistently flows by a certain spot in the 
earth's orbit. Whenever the earth passes by that spot, 
as it does at a given time every year, it is besprayed 
with meteors. 

The meteoric river does not have a source and a 
mouth as terrestrial rivers have. Its source and mouth 
are united, the entire stream being a vast ellipse within 
which the sun lies. In some parts of the stream the 
meteors are more thickly crowded together than in 
others. Whenever the earth dashes into a dense por- 
tion, the shower is unusually magnificent. A stream is 



Comets and Meteors. 291 

broader in some places than in others ; when the earth 
plunges into a broad portion the shower may begin be- 
fore its usual time. The meteors in some streams are 
mostly massed in a vast shoal, instead of being distrib- 
uted around the orbit. 

The August meteors are most numerous about the 
tenth of the month ; but the meteoric river is so 
broad that the earth takes over a month to go through 
it. Night after night, from July 18 to August 22, some 
meteors belonging to this aggregation may be observed. 
Their radiant is in Perseus. There are occasional gaps 
in the stream, so that some years bring no August dis- 
play worthy of the name of a shower. The elliptical 
orbit in which the meteors move extends beyond Nep- 
tune, and the stream requires over one hundred years 
for a single revolution. 

The shower of November 13 emanates from the con- 
stellation Leo ; the meteors are therefore known as Le- November 13. 
onids. Generally the display is not at all brilliant ; but 
once in thirty-three years it is of wonderful splendor. 
The first recorded appearance of this shower was in 902 
A. D., which was long known as " the year of the stars." 
For during the night in which the ancient Sicilian city 
of Taormina was captured by the Saracens, men saw 
"as it were, lances, an infinite number of stars, which 
scattered themselves like rain to right and left. ' ' 

An imaginative Portuguese chronicler relates that in 
the year 1366, " three months before the death of the of 1366. 
king Dom Pedro, there was in the heavens a movement 
of stars such as man never before saw or heard of. At 
midnight and for some time after, all the stars moved 
from the east to the west, and after being collected to- 
gether, they began to move, some in one direction and 
others in another. And afterward thev fell from the 



2g 2 A Study of the Sky. 

sky in such numbers, and so thickly together, that as 
they descended low in the air, they seemed large and 
fiery, and the sky and the air seemed to be in flames, 
and even the earth appeared as if ready to take fire." 
On November 12, 1833, the falling stars were as thick 
The display as snowflakes ; many were brighter than Venus. The 

of 1833. ' J & 

negroes in the Southern States were struck with terror, 
believing that the end of the world was at hand. They 
groaned, wept, prayed, and rolled on the earth, in 
ecstasies of terror. 

The year 1866 brought another fine shower. The 
next date on the program is 1899. The length of the 
dense part of the meteoric stream is 2,000,000,000 
miles, and it occupies nearly two years in passing any 
given point. The year 1898 may therefore furnish a 
fine shower. The periodic time of this shower is 33^ 
years. The direction from which the meteors come 
is nearly opposite to that in which the earth moves : 
they travel at the rate of twenty-six miles a second, 
while the earth has a velocity of eighteen miles a 
second. The effect is the same as if the earth were at 
rest, and the meteors hurled themselves against it with a 
velocity of forty-four miles a second. Such missiles, 
if not checked by the air, would go from New York to 
Chicago in twenty seconds. It is not astonishing that 
the meteors are bright and leave vivid trails behind 
them. 

In the latter part of November comes another shower, 
the radiant of which is in the constellation of An- 
dromeda. The meteors pursue the earth and overtake 
it ; because of this they do not rush into the air with the 
impetuosity which characterizes the Leonids. Their 
trains are short and of a reddish hue. In 1872 some of 
them looked as large as the moon ; in 1885 and 1892 



Another No- 
vember shower. 



Comets and Meteors. 



293 



there were fine showers ; another is expected in 1898 or 
1899. This shower derives special interest from its sup- 
posed connection with Biela's comet. The meteors pur- connection 
sue the same orbit as the lost comet, and it is possible Smet Blelas 
that they are the products of its disintegration. During 



r * ^ . \ |r '^," 






■' . • % . ■ 


1 


^ '•■ % • ' * 














- % 




* '• " ' ' '*' ' '• % \ '" J 




% 




■ yj , -f 




..T ^- l -V :: -v'- '"•*,-• v*;.***; 


, X V v ':v^- .^ 




** ' ! 


< %% ' i"i 




;:>,. ■ j 
•1 


L.x_ ^ ' ..X A/ 







Fig. 131.— Photograph showing a Meteor's Path among 
the Stars. 

the 1885 shower there fell at the town of Mazapil in 

, , . f . 1 ■ • 1 1 1 The Mazapil 

Mexico a piece of meteoric iron, which may have been a meteorite, 
piece of the comet. In 1892 the meteors came on 
November 23, instead of November 27, the date usually 
assigned ; this was due to a disturbance of the meteoric 
orbit caused by the attraction of Jupiter. 



294 



A Study of the Sky. 



Relation be- 
tween comets 
and meteors. 



The zodiacal 
light. 



There are other instances of a connection between a 
meteor-shower and a comet. The orbit of the August 
meteors is identical with that of the bright comet of 
1862. The great thirty- three year shower of Leonids 
follows hotly on the trail of Tempel's comet. 

The relation between comets and meteors is therefore 
intimate. A comet is a group of small bodies somewhat 
compacted ; a meteoric shower is caused by a group of 
small bodies more widely separated. The change which 
took place in the nucleus of the great comet of 1882 is 
one of many instances of the disruptive power which the 
sun exercises upon comets ; its tidal action upon them 
tends to scatter the bodies of which they are composed. 
These bodies when scattered cause a meteoric shower, 
if they collide with the earth. 

Akin to meteors and comets is the zodiacal light, 
which is a hazy white beam of light, best seen early on 
a spring evening. Resting on the western horizon it 
slants upward toward the south. In the tropics it is 
seen as a light girdle encircling the sky. It lies in the 
zodiac and is surmised to be an envelope of meteors 
surrounding the sun, after the fashion of a huge lens. 



METEORITES. 



Appearance of a 
flying fire-ball. 



The term meteors includes both shooting stars, which 
we have already considered, and meteorites. .The latter 
are bodies of such size and toughness that they can 
pierce the earth's atmosphere and find a resting place 
upon its surface. The flight of a large meteorite is sig- 
nalized by striking phenomena. If it come in the night 
time, it is a splendid fire-ball followed by a naming 
train ; there is a roar like that of the sea in a storm, ac- 
centuated by occasional detonations. In a few seconds 
there remains only a luminous streak of glowing ma- 



Comets and Meteors. 295 

terial, which has been wiped off from the exterior of the 
meteorite, as it dashed through the aerial furnace. 

The intensity of the heat which a meteorite ex- Atremendous 
periences may be imagined from the appearance of a fire - bal1 - 
fire-ball which was seen in England in 1869. The fiery 
envelope which enswathed it was more than four miles 
in diameter, and the entire body was consumed in five 
seconds. A cloud of glowing vapor fifty miles long was 
visible for nearly an hour. 

Sometimes a meteorite traverses a course hundreds of 
miles in length before the steady pressure of the air 
triumphs and brings it to the earth. Usually it breaks 
into numerous fragments while flying, and descends as a 
shower of stony missiles. 

The fragments do not penetrate the earth as deeply Destructive 
as would a projectile hot from the mouth of a rifled gun. P° wers - 
Still their destructive powers are by no means to be de- 
spised, for they have been known to kill men and to de- 
stroy buildings. Very few such catastrophes have been 
recorded, because buildings and men cover a very small 
part of the earth, and meteorites are infrequent visitors. 

Meteorites have been known to come to earth so 
quickly that the heat to which they were exposed had 
not time to penetrate their interiors. A meteoritic frag- 
ment, which once embedded itself in a moist spot of 
ground in India, was found half an hour afterward coated 
with ice. 

The appearance of a fallen meteorite testifies loudly to 
the experience which it has passed through. Most of fallen meteorite. 
these objects are stones which have thin crusts pro- 
duced by the fusion of their surfaces. In case a meteor- 
ite bursts just before it is brought to rest, the freshly 
cracked surfaces, having been exposed to very little 
heat, preserve their roughness, and may be fitted to- 



Coated with 
ice. 



Appearance of a 



296 



A Study of the Sky. 



Their compo- 
sition. 



Old records. 



A rare tract. 



gether again. Some parts of the stony masses are often 
softer than others, and are quickly fused and swept away 
into the meteoric train. The captured meteorite is then 
pock-marked with numerous pits. 

In all large collections of these bodies are a few com- 
posed of iron alloyed with nickel ; some of them are 
very formidable projectiles weighing several tons. 
Stony meteorites often have bits of iron scattered 
through them ; iron meteorites frequently have pockets 
laden with stone. These combinations are not limited to 
meteorites, but are also found in such basaltic rocks as 
those of the Giants' Causeway. 

Chemical analyses of meteorites have brought to light 
no new element ; twenty-five elements have been found, 
most of which are common on the earth ; the precious 
metals have not been discovered. Meteoric stones are 
composed of minerals, which are abundant in terrestrial 
rocks of volcanic origin. 

In 1 89 1 some 300 fragments of meteoric iron were 
found in the Canon Diablo in Arizona ; minute diamonds 
were embedded in them.* 

There are hundreds of accounts of falls of meteorites 
during the past 2,500 years. The Greeks and Romans 
considered them as celestial omens, and kept some of 
them in temples. One at Mecca is adored by the 
faithful. The emperor Jehangir is said to have had a 
sword forged from a meteorite, which fell in 1620 in the 
Punjab. An Ohio Indian mound has yielded up copper 
earrings plated with meteoric iron. 

We subjoin four interesting accounts of meteorites. 
The first is taken from a rare tract preserved in the 
British Museum ; its opening sentences are : 



* The diamonds were used at Tiffany's 
Chicago for polishing other diamonds. 



ivilion in the World's Fair at 



Comets a?id Meteors. 297 

So Benummed we are in our Senses, that albeit God him- 
selfe Holla in our Eares, wee by our Wills are loath to heere Heedlessness, 
him. His dreadfull Pursiuants of Thunder and Lightning ter- 
rifie vs so long as they have vs in their fingers, but beeing off, 
we dance and sing in the midst of our Follies.* 

After moralizing at some length the author narrates 
the event which has inspired his pen : 

The name of the Towne is Hatford, some eight miles from 
Oxford. Upon Wensday, being the ninth of this instant 
Moneth of April 1628, about five of the clocke in the afternoone 
this miraculous prodigious and fearefull handy-worke of God 
was presented. ... It beganne thus : First for an onset 
went off one great Cannon as it were of thunder alone, like a 
warning peece to the rest that were to follow. Then a little 
while after was heard a second : and so by degrees a third, on- 
till the number of 20 were discharged (or there-abouts) in very 
good order, though in very great terror. In some little dis- 
tance of time after this was audibly heard the sound of a Drum 
beating a Retreate. Amongst all these angry peales shot off 
from Heauen this began a wonderful admiration, that at the 
end of the report of euery cracke, or Cannon-thundering, a 
hizzing Noyse made way through the ayre, not unlike the fly- A " hizzing- 
ing of Bullets from the mouthes of great Ordnance : and by Noyse - 
the judgment of all the terror-stricken witnesses they were 
Thunderbolts. For one of them was seene by many people to 
fall at a place called Bawlkin Greene, being a mile and a half 
from Hatford : Which Thunderbolt was by one Mistris Greene 
caused to be digged out of the ground, she being an eye-wit- 
nesse amongst many others of the manner of the falling. The 
form of the Stone is three-square, and picked in the end. In 
colour outwardly blackish, somewhat like iron : crusted over 
with that blacknesse about the thicknesse of a shilling. Within 
it is a soft, of a grey colour, mixed with some kind of minerall, 
shining like small peeces of glasse. 

A detonating fire-ball, no fragments of which came to 
the ground, was seen on December 21, 1876. From fire-ball, 
some point in Kansas it sped to Niagara Falls, travel- 



A detonating: 



See Lockyer's " Meteoritic Hypothesis," pages 5-7. 



; 



_— _- — 




._ I3 2.-A Meteorite seen July 27, 1894- 



Comets and Meteors. 299 

ing at the rate of ten miles or more a second. When 
passing over Illinois it exploded, and formed a cluster of 
fire-balls which occupied a space forty miles long and j^JJSS" of 
five miles broad. Several minutes after the inhabitants 
of Bloomington saw the stream of fire-balls coursing 
past overhead, they were startled by a thunder-peal, 
which fairly shook the town, and led some to believe 
that a miniature earthquake was in progress. Sound 
travels a mile in five seconds, and the explosion was 
heard in Bloomington fifteen minutes after the disrup- 
tion of the meteor occurred. The sound of the ex- 
plosion must have traveled 180 miles before it smote 
upon the ears of the people of Bloomington. Had the 
fiery visitor come within eighteen miles of Bloomington 
instead of 180, how appalling the thunderings, which 
would have been multiplied a hundred fold ! Fortu- 
nately it was at an altitude of seventy-five miles when it 
was first seen, and kept at a great height, finally 
escaping from the air after it had passed Niagara Falls. 
Brenham township, Kiowa County, Kansas, was 
visited by a shower of meteoric iron at some time be- An iron hail, 
fore white men had established themselves there. From 
time to time the early settlers plowed up these curious 
pieces of iron. Though the people called the strange 
masses meteors, they did not realize their pecuniary 
value. A cowboy, however, attempted to carry some 
off, but his pony was unequal to the task. He therefore 
buried them, expecting to return at some future time ; 
but death frustrated his plan. A good woman, who 
was unable to persuade her relatives of the value of 
these chunks of iron, finally took matters into her own 
hands, sent for a college professor, sold her meteors, 
and paid off the mortgage on the farm from the pro- 
ceeds. 



3°° A Study of the Sky. 

On February 10, 1896, a fire-ball exploded over the 
fir h e !b^n drid clt y °* Ma d r id, m tne middle of the forenoon. The 
sun was shining brightly, so that the celestial visitor 
was seen only as a swiftly moving cloud. There was a 
loud report, which caused a panic in schools and facto- 
ries, and thus led to the injury of several people. Many 
windows were shattered, and a partition wall in a build- 
ing occupied by the United States legation collapsed. * 



So said the newspapers. 



& 



CHAPTER XVII. 

THE FIXED STARS. 

" Ye stars ! bright legions that, before all time, 
Camped on yon plain of sapphire, who shall tell 
Your burning myriads, but the eye of Him 
Who bade through heaven your golden chariots wheel ?" 

— Croly. 

The number of stars visible to an average eye on a 
ood night is not far from 2,000. Near the horizon 
faint stars are blotted out by atmospheric vapors. If 
we could see all the stars on the celestial sphere as well 
as we see those near the zenith, 6,000 would be visible 
without optical aid. A spy-glass brings out thousands 
otherwise unseen. By the largest telescopes millions 
are revealed ; hundreds of millions are sufficiently bright 
to record themselves on photographic plates. 

The Milky Way or Galaxy has been previously de- 
scribed as the beautiful river of light which flows across 
the sky, embracing a countless host of faint stars. One 
of the most interesting parts of it is in the south, when 
the summer twilight has faded. The Galaxy there di- 
vides for a portion of its length into two roughly parallel 
streams, and glows in places, as if illuminated by cos- 
mical fires. 

A marvelous complexity of structure is brought out by 
photographic plates exposed for several hours. There 
are curious curved lines of stars, vast cloud-like forms, 
long narrow lanes, and dark spots of various shapes. 

Tree-like forms, similar to those of some solar promi- 
sor 



Their number. 



The Galaxy, 



Complexity 
of structure. 



Tree-like forms. 



302 A Study of the Sky. 

nences, are of not infrequent occurrence ; some of them 

are dark, and some bright. They have been supposed to 

be analogous to solar prominences, not only in form, 

but also in origin. According to this view they are due 

so*™., to stupendous 

t —\ • uprushes into a 

"•."• resisting medium. 

, \ f\ ', '. The dark forms 

': 0. % v • ; may be caused 

• . •.*"'*•■•,.> vV'* by an absence of 

Y'-\ %-x'C'i matter, or by the 

presence of vast 

masses of absorb- 

ing material, 

which obscure 

the stars lying 

BAST. , 

beyond them. 

Naked-eye 
stars are distrib- 
uted over the 
entire celestial 
sphere with con- 
siderable uni- 
formity, but 

Y« f^^, /' those whlch are 

■ ■■ - >>^- *^^~;.r-..-^* . "*" invisible without 

s'"y l y .Z.'-./ .-J Jr. • telescopic aid are 

Fig. 133.— Outlines of Dark Structures arranged very 

in the galaxy. differently. They 

are most thickly crowded in the Milky Way. On either 
the skv Uti ° n in S ^ e °* xt t ^ ie numDer m a given area is less. The further 
one goes away from the Galaxy, the fewer the tele- 
scopic stars are. If we call the Milky Way the galactic 
equator of the celestial sphere, a given area in it con- 




The Fixed Stars. 303 



tains on the average thirty times as many stars as an 
equal area at either galactic pole. 

We have already learned how the stars are divided 
into constellations, how they are named, how their bright- A photographic 

■> ' fe catalogue. 

ness is estimated in magnitudes, and how catalogues of 
them are made. The greatest of all star catalogues is 
now being formed by the aid of photography. A num- 
ber of observers scattered over the world have united to 
photograph the entire heavens, using instruments of the 
same size and construction, and after the photographs 
have been taken several years will be required to meas- 
ure them and to prepare the results for publication. 

Astronomers are far from being content with making 
catalogues or maps of the stars. They wish to know 
how far they are away, what their dimensions are, of 
what substances they are composed, how they change 
appearance, how they move, what relation they bear to 
our sun, and what their origin and destiny may be. Let 
us take a glimpse of what has been done along these 
lines. 

In order to measure the distance of a star a base line 

r 1 1 1 1 -111 „n a 1 • Measurements 

01 known length must be available. When an Atlantic of distance. 

liner passes by a lighthouse, a man at the prow sees the 

lighthouse in a direction different from that in which a 

man at the stern sees it. If they knew the length of the 

ship, and had suitable instruments for measuring angles, 

they could find the distance from the lighthouse to 

either one of them, at a given instant. 

If two astronomers, one in northern Russia, the other 
at the Cape of Good Hope, should both look at the 
moon at the same instant, it would appear to them to lie 
in slightly different directions, and they could calculate 
its distance. But if they were to try the same plan with 
a fixed star they would be balked because no instru- 



304 



A Study of the Sky 



A long base 
line. 



ments are sufficiently delicate to measure the very slight 
difference between the directions in which the two men 
see the star. A longer base line must be used than the 
distance from St. Petersburg to the Cape of Good Hope. 
If an astronomer measure the right ascension and de- 
clination of Sirius on January i and again on July i, 
when the earth has gone half way around its orbit, to a 





i2.:.Lii:' _L 




Fig. 134.— A Part of the Milky Way in Cygnus. 



The nearest 
star. 



point 186,000,000 miles distant from its former position, 
he will find that Sirius has apparently changed its posi- 
tion slightly, on account of the observer's change of 
view-point. With the aid of a little mathematics the 
celestial surveyor computes the distance to Sirius. 

Most of the stars are at such inconceivable distances 



The Fixed Stars. 305 



that even the base line of 186,000,000 miles is insuffi- 
cient. Our nearest neighbor, so far as present knowl- 
edge goes, is Alpha Centauri, which is 275,000 times as 
far away as the sun ; its distance is over 25,000,000,- 
000,000 miles. Sirius is twice as far away, and light 
takes eight years to come from it to us. The pole-star 
shines by light which left it fifty years ago. 

No one has yet been able to measure directly the 
diameter of any star, on account of their amazing 
distances. Though the sun's diameter is 860,000 miles, 
it would look to an eye near Sirius as small as a 
marble 2,000 miles away. Yet we can get a rough 
estimate of the probable size of a star, the distance of 
which is known, by measuring the amount of light 
which it emits. Capella and Vega are thought to be 
much. larger than the sun. Some are so bold as to 
estimate that Arcturus is 1,000,000 times as large as 
the sun ; but such an estimate must be considered very 
insecure. When two stars are close together and re- 
volve about their common center of gravity, the swift- 
ness of their motion combined with their distances from 
us and each other gives a clue to their masses. Periodic 
shiftings of the lines in a star's spectrum also furnish 
evidence, which we cannot here detail. 

Mizar at the bend of the handle of the Great Dipper 
is thought to be at least forty times as massive as the 
sun. Algol is periodically eclipsed by a dark body 
revolving about it. From the length of the eclipse, 
combined with other data obtained spectroscopically, 
a diameter of 1,000,000 miles has been figured out 
for it. 

No star sends us a measurable amount of stellar heat ; 
the entire body of stars gives one sixtieth as much light 
as the full moon, and decidedly mitigates the darkness 



The sizes of 
stars. 



Stellar heat. 



306 A Study of the Sky. 

of the night. Seven billion stars like Sirius would be 
required to make night as bright as day now is. 

DOUBLE STARS. 

Double stars exist in considerable numbers, 10,000 
being catalogued. Many more have been seen, but 
adjudged to be too faint to deserve attention, until their 
brighter brethren have been investigated. A double 
star appears as one to the naked eye, but is split up, by 
telescopic or spectroscopic aid, into two stars. 

An optical double is one the components of which are 
optical not really close together ; one of the two components 

lies far beyond the other, but in nearly the same line of 
sight. 

In a physical double star, or binary, the two stars are 
pinsicai neighbors subject to dne another's attraction. Each of 

doubles. & ill- r 

the two stars revolves about their common center 01 
gravity. Such a system is unlike ours, where a number 
of comparatively small and cool bodies revolve about a 
large hot body. In a binary system there are two suns, 
often equal in size, which revolve like partners in a 
waltz. Each of them may be surrounded by a troop of 
planets for aught we know. If Jupiter were transported 
to the vicinity of Alpha Centauri, and became a planetary 
attendant upon it, the largest telescopes would seek for 
it in vain. 

It is not yet known that the force of gravitation, 
Does gravity which keeps the planets in their orbits, controls the 

bind binaries? . , .. ^ i_ „_i • 1 -j 

motion 01 binary stars, but there is so much evidence in 
favor of this supposition that it is accepted as a fact. 
Since the spectroscope shows that the stars are com- 
posed of elements found on the earth and the sun, as 
well as in other planets, comets, and meteors, there is 
no good reason for thinking that the same materials, 



The Fixed Stars. 307 



when found in the stars, will not attract each other 
according to the same law which we observe in the solar 
system. When the orbits of double stars are computed 
upon the assumption that their motion is due to the 
force of gravity, and when their relative positions are 
predicted for years to come, the predictions are verified 
by the motions actually observed. A mass of evidence 
is continually accumulating to show that physical, 
chemical, and mechanical laws, discovered by experi- 
mentation upon terrestrial bodies, hold good throughout 
the visible universe. 

The history of the discovery of the duplicity of Sirius 
strengthens the view that the universe is a wonderful 
unit, subject throughout its wide extent to laws which 
are the expression of the will of its Creator. During the 
first half of the nineteenth century thousands of accurate 
observations of the right ascension and declination of 
Sirius were made. The more earnestly accuracy was 
sought, the more impossible it was to make the observa- 
tions agree with one another. It became evident that 
Sirius was not fixed on the face of the sky. 

More than half a century ago the illustrious German 
astronomer Bessel attacked the problem, and announced 
that Sirius was moving in a tiny curve, and that this 
curvilinear motion was probably a case of orbital revolu- 
tion, in which an unknown companion took part. A 
few years afterward two other German astronomers 
made a yet more thorough discussion, and reached the 
conclusion that the companion made a complete revolu- 
tion in fifty years. They also pointed out the direction 
in which the companion then lay from Sirius, and the 
direction in which it was moving. Eight years later 
their confidence was rewarded by the discovery of the 
disturbing body by Alvan G. Clark, who was not aware 



Sirius. 



A curvi 
motion. 



A companion. 



Spectroscopic 
doubles. 



308 A Study of the Sky. 

of the prediction made by the two Germans. The com- 
panion is not to^oo as bright as the main star, but it 
is one half as heavy. It is therefore a much cooler 
object than Sirius, and may in the course of ages be- 
come a genuine planet, though an enormous one. 

Perhaps the most interesting class of double stars 
embraces those in which the two components are so 
close together that they can never be separately seen. 
Though the two may be equal in size and brightness, 
they look like one perfectly round body, no matter how 
high the magnifying power employed. Their existence 
becomes known through the spectroscope. If the 
bodies are just alike, each of them gives a particular 




£artli 



3 
Fig. 135.— Motion of the Components of a Double Star. 



spectrum ; if they are at rest the two spectra coincide ; 
but if they are in motion in a plane turned nearly edge- 
wise to us, one body at a certain point in its orbit is 
moving away from us quite rapidly, while the other is 
approaching. This is the state of affairs when the 
bodies are at A and B, Fig. 135. 
shiftin of ^he nnes m tne spectrum of one body are therefore 

the lines. shifted in one direction, and the corresponding lines in 

the other spectrum move in the other direction. At the 
instant when the bodies are at C and D respectively 
neither of them is being carried by its orbital revolution 
toward the earth or away from it. The spectral lines are 
therefore not shifted by the orbital revolution at that time. 
When the stars are at C and D their spectra coincide; 
when they are at A and B the spectra are separated, and 



The Fixed Stars. 309 



Multiple stars. 



corresponding lines, which formerly coincided, now 
stand side by side. In a word, the dark lines some- 
times appear single and sometimes double, the doubling 
recurring at regular intervals. 

Spica, in Virgo, is a rapid spectroscopic binary, the 
revolution being completed in four days. If the com- 
ponents are equal they are but 6,000,000 miles apart, and 
each is a third heavier than the sun. 

A system not infrequently contains three or more re- 
volving suns. An interesting quadruple system is found 
in Epsilon Lyrse, one of the faint stars near Vega. It 
has already been described under the constellation Lyra. 
Theta Ononis, which is in the great nebula in Orion, is 
a sextuple star. There are many instances of multiple 
stars, where several are grouped together. Stars in a 
given group may be really close together, so as to form 
a revolving system, or they may be like optical doubles, 
in which one star is a great ways beyond the other. 
Zeta Cancri is composed of three visible stars, two of 
which are close together and constitute a binary system. 
The third star seems to revolve about the binary, but its 
motion is subject to irregularities, thought by some to 
be due to an invisible member of the system. 

STELLAR SPECTRA. 

When stars are examined with the spectroscope, great 
diversities between them become apparent. The spectra 
are so various that it is impossible to make a satisfactory 
classification of them. Yet by considering only certain 
broad characteristics a few types may be distinguished. 

Type I. This type embraces the white or bluish stars, sirians. 
which are far more numerous than others. Sirius, Vega, 
and Altair belong to it, and the entire group is often 
called Sirian. The principal lines in the spectrum are 



3io 



A Study of the Sky. 



Solars. 



Variables. 



Deep red stars. 



Bright-line 
stars. 



due to hydrogen ; other lines are faint and few. Two 
thirds of these stars are in the Milky Way. 

Type II. Yellowish stars having spectra similar to 
that of our sun are placed under this head ; such are 
Pollux, Capella, and Arcturus, which are called solar 
stars. The spectrum is rich in lines belonging to vari- 
ous metals. Solar stars are distributed equably over 
the heavens. The light of a Sirian star is more in- 
tense than that of a solar, but the latter gives on the 
average a greater quantity of light, because of its greater 
size. 

Type III. Orange and red stars, together with most 
of those which fluctuate in brightness, belong to this 
class, which includes Betelgeuse and Antares. Their 
spectrum contains many dark bands, one edge of which 
is sharply defined, while the other is diffuse ; the sharp 
edge is on the side next to the violet end of the spec- 
trum. 

Type IV. The stars belonging to this type are few in 
number, faint, and generally of a deep red color. The 
spectrum is banded as in Type III. , but the sharper edge 
of each band is on the side next to the red end of the 
spectrum. 

More than fifty stars have been discovered, whose 
spectra are different from any of the preceding, in that 
they contain bright lines, thought to be due to extensive 
gaseous envelopes enwrapping them. They are of 
especial interest because they seem to form a connecting 
link between nebulae and other stars. Bright lines, 
thought to be due to masses of vapor hotter than the 
underlying photosphere, are at times seen in the spec- 
trum of the sun. Most of the stars in Orion exhibit a 
special variety of spectrum, which is not often met out- 
side of that constellation. 



The Fixed Stars. 311 



So many different varieties of spectra are known that The universe 
Prof. E. C. Pickering * says : 

In general it may be stated that with a few exceptions all 
stars may be arranged in a sequence, beginning with the 
planetary nebulae, passing through the bright-line stars to the 
Orion stars, thence to the first type stars, and by insensible 
changes to the second and third type stars. The evidence that 
the same plan governs all parts of the visible universe is thus 
conclusive. 



Is development 



The opinion that different spectra belong to different 
stages of development has much in its favor, but more indicated? 
complete investigations must be made before any far- 
reaching theory can command the entire consent of 
spectroscopists. 

VARIABLE STARS. 

Many stars are inconstant in brightness, and bear the 
designation of variables ; the number of known variables 
is now (1896) nearly four hundred, but new ones are 
being found continually. Certain compact clusters con- 
tain a large number of variables. They are not included 
in the number specified above. 

The most marvelous class of variables is the tern- Temporary 
porary stars which appear occasionally, often blazing up 
with a wonderful display of luminous energy, and then 
fading into insignificance, or entire invisibility. Per- 
haps the most famous of these is Tycho's star, which he 
perceived while out walking on a November evening in 
1572. It was in the constellation of Cassiopeia, and 
was nearly as bright as Venus at her best. For several 
days it was visible in broad daylight, but began to lose 
its splendor in December ; fifteen months later it was 
too faint to be seen. Tycho measured its place as well 
as it could be done without the aid of a telescope, 

* Director of the Harvard College Observatory. 



stars. 



312 



A Study of the Sky. 



Nova Auric 



A strange 
spectrum. 



which had not then been invented. There is now a 
faint star near the place assigned by him, but it is not 
certain that the two objects are the same. 

The most remarkable recent temporary star is Nova 
Aurigse (the new star in Auriga). It was first seen by 
an amateur Scottish astronomer on January 24, 1892, 

being then of 
the fifth magni- 
tude. It had, 
however, previ- 
ously impressed 
itself on a pho- 
tographic plate 
exposed at Har- 
vard on Decem- 
ber 10, 1891. It 
was not on a 
p h o tograph of 
the same region 
made at Heidel- 
berg on Decem- 
ber 8. It must 
therefore have 
burst out sud- 
denly between 
these two dates. 
Its spectrum 

[36. — A Rich Portion of the Milky Way. 

was at once in- 
vestigated : two spectra were found ; one was a bright- 
line spectrum, the other an absorption or dark-line 
spectrum. The lines in the two spectra were not in 
their normal positions, but were shifted in such a way 
as to indicate that there were two bodies moving in 
different directions. During February and March the 




Fig. 



The Fixed Stars. 313 



brightness of Nova fluctuated irregularly ; after March 
6 its magnitude diminished rapidly, and in six weeks it 
was barely visible in the Lick telescope. Four months 
afterward it was bright enough to be seen in a three- 
inch telescope, and looked like a small round nebula. 
The shifting positions of the spectral lines denoted large 
and variable velocities, and are very difficult to explain. 

One hypothesis as to the cause of the outburst is that 
two large bodies moving swiftly barely missed colliding, Cause of the 
and created great tidal disturbances, which in turn led 
to tremendous eruptions similar to solar prominences, 
but on a vastly greater scale. Another theory is that a 
dark body plunged into some cosmical cloud, like the 
vast nebulous masses, which photography reveals here 
and there. When it passed out of the cloud in the 
spring it rapidly cooled off ; in the fall it encountered 
another such cloud, which brightened it up again. The 
observations are, however, too complicated to be ex- 
plained fully by any hypothesis yet advanced. 

Very different from a temporary star is Algol, the 
Demon Star, so named by the ancients ; it is in the 
constellation Perseus. Usually it is a star of the second 
magnitude, but at regular intervals of 2 d - 2o hrs - 48"""- 
56 sec - it drops to the fourth magnitude ; it remains faint 
for only twenty minutes, and brightens again until it 
reaches its usual luster. Its light is varying during 
9 hrs - 45 min - of each period. The periodical darkening is 
a partial eclipse caused by a dark body revolving about 
a bright one : this is rendered practically certain by 
spectroscopic measurements, which show that Algol 
alternately retreats from us and approaches us, just as 
if it were one star of a revolving system. The dark 
companion is computed to be of nearly the same size as 
the sun ; the main star has a diameter one fifth greater. 



Algol. 



Mira. 



314 A Study of the Sky. 

The distance between their surfaces is only 2,000,000 
miles. Less than a dozen variables, which suffer eclipse 
like Algol, are known. 

Mira (the marvelous) is a strange variable located in 
Cetus ; its changes have been observed for three hun- 
dred years. It occupies eleven months in running the 
gamut of its variations. During most of this time it is 
invisible to the naked eye, though an opera-glass shows 
it ; but once in eleven months it rises in a few weeks to 
a maximum brightness, remains thus for about a week, 
and then sinks back slowly to its former faintness, the 
entire change occupying three months and a fraction. 
Sometimes its greatest brilliancy does not equal that of 
the faintest of the seven stars in the Great Dipper ; at 
other times it rivals the brightest of them. At the time 
of a maximum its spectrum glows with a profusion of 
bright lines. The strange behavior of this star 
and others of its class may be explained by periodical 
eruptions like the solar prominences, though on a much 
larger scale. The periodicity of such eruptions is as 
mysterious as that of sun-spots, 
irregular There are variables which are unlike Algol or Mira, 

some of them being seemingly hopelessly irregular in 
their variations. The cause of their variability can only 
be conjectured. They may be afflicted with enormous 
spots, or subject to collisions with meteoric streams ; 
great protuberances may also complicate matters, while 
rotation upon an axis may tend to give a certain regu- 
larity to the variations. 

Aggregations in which the stars are to be counted by 
tens or hundreds of thousands are known as clusters. 
Several of the stars in the cluster of the Pleiades can be 
seen with the naked eye, and many more are brought 
out by an opera-glass. Praesepe in Cancer and the 



variations. 



Clusters. 



The Fixed Stars. 



315 



double cluster in Perseus look like bright spots on the 
sky, and are split into separate stars by a small telescope. 
All these are coarse clusters. 

The finest compact cluster in the northern hemis- 
phere is located in Hercules. One who knows just 




Fig. 137.— The Great Globular Cluster in Hercules. 

where to look for it can see it as a hazy faint star. A 
large telescope is needed to resolve the entire cluster 
into separate stars. It is globular in form, and near its 
center the stars appear fairly to touch one another ; at 
the edge the stars are more scattered, and branch out 
in pretty sprays. Such a cluster has been called an 
"island universe," as though it were a system apart 



The great 
cluster in 
Hercules. 



An " island 
universe." 



rejected. 



316 A Study of the Sky. 

from other stars, sunk in well-nigh infinite depths of 
space ; according to this view the stars which appear so 
crowded are really separated by intervals comparable 
with the distance from the sun to Alpha Centauri or 
Sirius. If this were true a spectator on one of those 
distant orbs might look about him, and see a heavens 
like our own, spangled with novel constellations, and 
dotted here and there with clusters, one of which con- 
tained our own sun and the bright stars familiar to us. 

The theory But this theory is no longer held. In certain parts of 

the heavens clusters, nebulae, and individual stars of va- 
rious degrees of brightness are so associated that there 
is little probability that the clusters are isolated groups 
lying at inconceivable distances beyond the other ob- 
jects. 

In the great Hercules cluster each star must be sub- 
ject to the gravitating influence of the others ; but no 
motion has been detected yet. Photography may event- 
ually lead to the detection of changes. The general 
opinion is that the cluster in Hercules, and others of 
similar appearance, are composed of much smaller stars 
than the sun. 

is the universe If it were possible to survey the sidereal universe 
from without, as now we look at the Hercules cluster, 
would it too appear globular ? 

The first fact to be considered is that the vast majority 
of the stars lie in the Milky Way, which forms a girdle 
around the celestial sphere. Now if we were near the 
center of a spherical cluster, like that in Hercules, 
throughout which the stars were distributed with any 
approach to uniformity, they would appear to be about 
equally numerous in whatever direction we looked. 
There would be no point within the sphere from which 
the vast majority of the surrounding stars would have 



spherical ? 



The Fixed Stars. 317 



the appearance of a ring like the Galaxy. We there- 
fore reject the hypothesis of sphericity and try again. 

Suppose that an aquarium is a circle ten feet in 
diameter, in which the water is a foot deep. The body illustration of 

an aquarium. 

of water has the shape of a thin cheese. Let the 
aquarium be well stocked with minnows, and let a 
single fish somewhere near the center look about him. 
When he looks horizontally, no matter toward what 
point of the compass, he sees a goodly number of his 
companions. If he looks straight up or down he sees 
comparatively few. If he looks obliquely upward or 
downward he sees more fish than when he looked 
straight up, and fewer than when he looked horizon- 
tally. If he had an agile brain and pondered over the 
matter, would he not conclude that the reason why he 
saw the most fish when looking horizontally, was that 
the aquarium extended farthest in that direction ? The 
more he studied the case the more confident would he 
be that the aquarium was cheese-shaped. 

Does not this illustration represent what an astrono- 
mer sees when he looks about? If he looks toward the 
Milky Way, which appears to surround him, he sees a 
large number of stars. It has been stated that the 
further he looks from the Milky Way the fewer stars 
he sees. Is it not reasonable then to suppose that the 
sidereal universe occupies a space shaped somewhat like 
a thin cheese or a silver dollar ? 

But more persistent inquiry will bring out some inter- 

, m 1 i- r 1 The solar 

esting facts. Those stars whose distances from us have cluster, 
been measured are mostly bright, and are scattered 
pretty evenly in all directions from us, showing no tend- 
ency to crowd together near the Milky Way ; their 
spectra are chiefly like the sun's spectrum. The sun 
therefore is a member of a cluster of stars similar to 



3i' 



A Study of the Sky. 



itself in composition and probably globular in form. 

The faint stars in and near the Milky Way are, almost 

Mik f °w of the without exception, at distances which defy our powers of 

measurement. Of faint stars of any particular order of 

brightness those 
near the Milky Way 
are in general 
further from us than 
those in other parts 
of the heavens. 
Shall we not say 
then that most of 
the stars in the 
Milky Way consti- 
tute a ring sur- 
rounding us ? Stars 
whose spectra are 
like that of Sirius 
are very abundant 
in and near the Gal- 
axy, and scattered 
sparsely in other 
regions ; this fact 
has led Professor 
Pickering to say 
that the Milky Way 
may well be regard- 
ed as "a distinct 
cluster of stars, to 
which, from its com- 
position or its age, the sun does not seem to belong. 
Saturn on a The mental picture of the stellar universe which 

springs from the preceding considerations rudely resem- 
bles the planet Saturn. Within is a ball of stars, of 




Fig. i 38.— Cloudy Region in the Milky Way. 



The Fixed Stars. 319 



which the sun is one. Surrounding the ball is an irregu- 
lar ring composed of faint stars in and adjacent to the 
Milky Way. Such a theory as this cannot be consid- 
ered final, but it commends itself as the best that can be 
devised in the light of present knowledge. 

Our next inquiry is about the motion of this stupen- 

. . . ., 1 t ... . f Proper motions 

aous system ; the only available light comes irom a of stars. 
study of the movements of a great many stars scattered 
in all parts of the heavens. Many stars are moving 
slowly across the face of the sky, despite their designa- 
tion of fixed stars. Star No. 1830 in Groombridge's 
catalogue moves a degree in five hundred years. Arc- 
turus, which also has a large proper motion, has shifted 
its position by an equal amount during the Christian era. 
Such rapid motions are quite exceptional. If a star is 
moving toward us or from us, its velocity of approach or 
recession is obtained by spectroscopic observations ; no 
velocity yet measured exceeds fifty miles a second. A 
star which is moving directly toward us, or away from 
us, has no " proper motion," because it does not alter 
its position on the face of the sky. 

Many groups of stars have a common proper motion. 

. Some groups 

Only a few out of four hundred stars in the Pleiades, whose have a common 

• -r motion. 

proper motions have been measured, refuse to drift along 
in the same direction as the others. It may almost be laid 
down as a principle that most of the stars in any group 
drift together, as though they were really connected. 

The stars are going in all directions, so that it seems 
impossible to deduce any general results about their 
movements. But patient study of large numbers of 
proper motions has clearly brought out a prevailing drift. 
Stars in Hercules and Lyra are spreading apart very 
slowly ; those on the opposite side of the celestial sphere 
are coming together. 



A prevailing 
drift. 



320 



A Study of the Sky 



Is there a 
central sun 



Various 
systems. 



Is there evi- 
denceof design? 



A passenger on a ferry-boat plying between two cities 
at night sees lights along the wharves of each city. The 
lights in one set are spreading apart ; in the other they 
are coming closer together. He knows at once that he 
is going toward the spreading lights. In like manner 
the astronomer concludes that the sun, carrying along 
its family of planets, is moving toward that region of 
the heavens which Hercules and Lyra grace. Whether 
the sun is moving in a straight line, or in the majestic 
sweep of some grand orbit, cannot yet be decided. 

There is a persistent idea that there exists a central 
sun, about which all the starry hosts move obediently 
in vast cycles of time. But the motions of the stars are 
so complex that no one can hope to locate a point about 
which all bodies in the universe revolve. 

There are hosts of subsidiary systems, which are 
orderly in their ongoings. The solar system is ruled 
despotically by the sun. Binary systems move in 
proper fashion, bound by a common tie. The stars 
composing a group like the Pleiades seem to be im- 
pelled toward a common goal. Thus the entire sidereal 
universe is composed of groups which are practically 
independent of one another. There is, in the present 
state of astronomical knowledge, no inkling of a general 
plan in accordance with which all the stars move. 

But the design of the Creator may not involve any 
particular form of orderly movement which the mind of 
man has yet conceived. The fact that the molecules 
which compose a marble statue do not revolve about a 
common center, or move in curves whose sinuosities 
can be embraced in a formula, does not detract from its 
beauty, or argue the absence of design. The entrancing 
beauty shines forth, and speaks eloquently of the cun- 
ning hand of the sculptor. 



CHAPTER XVIII. 

THE NEBULA. 

" Regions of lucid matter taking forms, 
Brushes of fire, hazy gleams." 

— Tennyson. 

Nebulae are cloud-like masses, of a great variety of 
form. Planetary nebulae are small and round ; they are classes of 



usually somewhat brighter in the center than at the 
edge. If there is a very marked central condensation, 
the object may be called a nebulous star. Annular 
nebulae are ring-shaped, brighter at the edge than near 
the center. Spiral nebulae exhibit coils, like those of a 
watch-spring, or a corkscrew. The largest nebulae are 
irregular in form and enormous in extent, being the 
largest visible objects in the universe ; they dwarf 
everything else into insignificance. Photographs of 
Orion show that a large part of the constellation is 
involved in a great nebula. Many clusters contain 
nebulous matter within their boundaries ; large nebulae 
often appear to shelter stars within their ample folds. 

About 8,500 are now known ; new ones are being 
continually discovered. Photography offers a distinct 
advantage for the work of discovery, since the sensitive 
film captures objects too faint to impress the eye. They 
are not scattered uniformly over the sky ; near the 
Milky Way few are to be found. Where stars are few 
nebulae abound, being most numerous near the galactic 
poles, as previously stated. 

No one has succeeded in measuring" the distance of a 



nebulae. 



Discovery and 
distribution. 



322 



A Study of the Sky. 



Distances. 



nebula, though repeated attempts have been made upon 
planetary nebulae. No nebula invites such an attack, 
unless it has some nuclear point which can be bisected 




Fig. 139.— A Spiral Nebula. 



Association 
with stars. 



with the spider-web of a micrometer. Yet they are 
in many cases so associated with stars that one cannot 
doubt that they are at the same distances. 



The Nebula. 323 



Changes. 



In the Pleiades nebulous wisps connect certain stars ; 
some of the brighter stars of the cluster are involved in 
nebulosity. The sextuple star Theta Ononis lies in a 
dark place in the great nebula in Orion. The appear- 
ance suggests that some of the adjacent nebulous matter 
has been used up in forming the stars. Four groups of similar spe ctra. 
lines in the spectrum of the stars coincide with corre- 
sponding groups in the spectrum of the nebula, and 
render it very probable that the stars actually lie in the 
nebula, instead of being merely in line with it. The 
nebula therefore is at the same distance as the stars. 

As spectroscopic observations have shown, their ve- Motions- 
locities are of the same magnitude as those of stars. 

Drawings of a given nebula made at the same time by 
observers using different instruments vary so much in 
detail that a comparison of one set of drawings with an- 
other gives no secure evidence of change in the form of 
the nebula. The case of the trifid nebula in Sagittarius 
deserves mention in this connection. It contains a 
curious dark rift, in which Herschel and other observers 
saw a triple star, in the early part of the nineteenth cen- 
tury. This star, which has not moved appreciably with 
reference to other stars in the vicinity, now lies in the 
edge of the nebulous matter adjacent to the rift. The 
nebula must either have changed its form or drifted. 
While the outlines of the central portion of the great 
nebula in Orion remain unchanged, there are anoma- 
lous variations in the brightness of different portions of it. 

Most of the nebulae are too faint to give perceptible 
spectra. About half of the spectra thus far examined Spectra, 
are composed of a few bright lines, which come from 
glowing gases. The presence of incandescent hydro- 
gen is amply demonstrated ; helium is fairly recognized, 
and also sodium. The remaining spectra are chiefly 



324 



A Study of the Sky. 



The Androm- 
eda nebula. 




Fig. 140. — The Nebula of 
Orion Photographed. 
Exposure, fifteen minutes. 



continuous bands of color such 
as would be given by heated 
liquid or solid bodies, or gases 
subjected to great pressure. A 
few nebulae give both spectra. 
Nebulae may contain solid or 
liquid bodies which are not suffi- 
ciently luminous to manifest 
themselves. 

The great nebula in Androm- 
eda is easily seen with the 
naked eye. A small telescope 
shows that it has a bright ball 
near the center, and is spindle- 
shaped. The magnificent pho- 
tographs taken of late years 
reveal a very interesting struc- 



ture. The whole rudely 
resembles Saturn, the cen- 
tral ball being surrounded 
by a ring ; in the ring are 
dark curved lanes, as 
though the structure was 
spiral. Two smaller balls 
outside of the ring sug- 
gest planets yet uncon- 
densed. There appeared 
in 1885 close to the nu- 
cleus of the nebula a new 
star which could be seen 
with an opera-glass ; in a 
few months it had van- 
ished. It was probably a 




Fig. 141. — The Nebula of Orion Pho- 
tographed. Exposure, two hours. 



The Nebula. 



325 



fortuitous condensation or local brightening of the nebu- 
lous matter, its spectrum being like that of the nebula. 
The great nebula in Orion is the most wonderful in 
the heavens. Its most brilliant portion is in the sword- 
handle of the giant. One easily sees there three stars 
in a row ; the middle star is surrounded by a feeble glow 



Fig. 142.— The Nebula of Orion Photographed. Exposure, nine hours. 

coming from the nebula. Galileo has left no record of it, 
much as he scoured the heavens. Cysatus, who was 
following a comet in 161 8, first came across it, and com- 
pared the comet with it. As telescopes improved, the 
star which it envelops was split into four, called the 
Trapezium ; later two more were added to the four. 
Dark spots were seen in the cloud, and enormous wing- 
like extensions of faint nebulosity, which gave the neb- 



The nebula 
in Orion. 




The Trape- 
zium. 



326 A Study of the Sky. 

ula the appearance of a ghostly bat of prodigious size. 
The spectroscope then revealed the bright-line spectrum 
of glowing gas, though portions of the nebula have 
square corners and bright ribs and dark vacuities. 
Finally photography scored a signal triumph by extend- 
ing the nebula in wraith-like arms which embrace a large 
part of Orion. Perhaps the exceptional richness of the 
constellation is due to the vastness of the nebular quarry 
from which the stars were hewn. 

" Where striving o'er the dim, ethereal plain, 
Orion brandishes his flaming sword, 
And shakes ajar the awful vestibule 
Of heaven's stupendous treasury of suns, 
Set for a jewel in the mighty hilt." 

The Magellanic clouds, or nubecula^, are invisible in 

The Magellanic . 

clouds. the United States, because they are too* near the south 

celestial pole. They resemble detached sections of the 
Milky Way, the larger one being of the size of the bowl 
of the Great Dipper, while the smaller is one fourth as 
large. These marvelous aggregations may well be 
likened to celestial show-cases, in which are displayed 
specimens of sidereal wonders. While nebulae and 
clusters fight shy of one another in other parts of the 
heavens, they are here mingled indiscriminately. Glob- 
ular clusters are found in all stages of condensation, and 
irregular clusters of various degrees of coarseness. Ir- 
regular nebulae of curious forms, and neat little elliptical 
ones, are thickly scattered over a background rich in 
stars. In places the stars are minute and packed as 
though they were the closely woven texture of a 
celestial fabric. 

A peculiar interest inheres in the study of nebulae, 

rial of worlds, since they are thought to be the chaotic world-stuff from 
which stars, clusters, suns, planets, and satellites have 



The Nebulce. 327 



been evolved. Milton adumbrates this idea in the 
second book of ' ' Paradise Lost, ' ' where he describes 
Satan pausing a moment at the open mouth of hell, ere 
he set out across the abyss which lay before him, seek- 
ing for the abode of man. 

" Into this wild abyss, 
The Womb of Nature, and perhaps her grave, 
Of neither sea, nor shore, nor air, nor fire, 
But all these in their pregnant causes mixed. 
Confusedly, and which thus must ever fight, 
Unless the Almighty Maker them ordain, 
His dark materials to create new worlds : 
Into this wild abyss the wary fiend 
Stood on the brink of hell, and looked awhile, 
Pondering his voyage : for no narrow frith 
He had to cross." 

Men may properly be abashed before the problem of 

1 r , • 1 ,1 The nebular 

the development 01 the universe, but they have not hypothesis, 
hesitated to attack it, working out a theory concern- 
ing the origin of the solar system, and following the 
same line of thought with reference to the countless 
bodies which make up the sidereal heavens. The 
famous hypothesis, which has been slowly elaborated 
during a century and a half, is familiarly known as the 
"nebular hypothesis." Suggested by Kant and Swed- 
enborg it was treated from a mathematical standpoint by 
Laplace at the close of the eighteenth century. Since 
that time it has undergone modification in details, but 
the outline of the original fabric of thought remains. 

According to this theory the materials which are now 
to be found in the sun and planets were originally of the solar mg 
diffused through a nebula of vast extent. The nebula 
may have been a mass of heated gas, but was probably 
a cloud of cold dust. The mutual attractions of its 
particles caused it to assume a globular form, to acquire 



328 A Study of the Sky. 

a rotatory motion, and to become hotter. The smaller 
it became, the more rapidly it whirled ; it was flattened 
at the poles and bulged at the equator. The ' ' cen- 
trifugal force ' ' finally became so great that the central 
attraction could no longer restrain matter in the equa- 
Ringsormore torial regions, and a ring escaped at the equator. Or 

compact masses 1 

are left behind, if there were some place on the equator where the 
matter was denser than in adjoining regions, a lump 
was formed at this dense spot, and the lump was left be- 
hind, instead of a ring. 

The original body rotated still more swiftly ; another 
Formation of ring or another ball was liberated. If some portion of 
planets. an a b anc [oned ring was markedly more dense than the 

rest of it, it gradually attracted to itself the adjacent 
matter, and finally formed another rotating body (a 
planet), which in turn threw off rings or balls of matter 
to form satellites. If a ring were pretty homogeneous 
it might condense into a multitude of bodies like the 
asteroids, or the rings of Saturn, which are by some 
considered an ear-mark of the creative process. 

A liberated ball would form a planet more quickly 
Further histor ^an a rm £ wou ^. The planets and satellites gradually 
of the planets, liquefied and solidified, falling in temperature at the 
same time. Minute bodies like the satellites of Mars 
lost their heat quickly, and are probably now solid 
throughout. On larger bodies a crust was formed, and 
the central fires have not yet died out ; such is the case 
of the earth. Still larger bodies, like Jupiter and 
Saturn, have probably not cooled off sufficiently to per- 
mit the formation of a solid crust. The sun, which 
holds in fiery embrace most of the matter in the original 
nebula, will begin to cool off whenever his huge mass 
begins to liquefy. 

Such is the nebular hypothesis, briefly stated. Some 



The Nebulce. 329 



years ago it was supposed that the retrograde motions 
of the satellites of Uranus and Neptune, and the rapid 
motion of the inner moon of Mars, which completes 
a revolution in less than one third of a Martian day, were 
objections to the theory. But these anomalies have 
now received satisfactory explanations. 

Let us now travel in imagination throughout the 




Objections. 



Fig. 143.— A Drawing of the Central Part of the Great Nebula 
in Orion. 

universe, investigating the nebulae, the stars, the earth, a broad inves- 
the moon, the planetary system, and finally the sun, tI s atlon - 
that they may give their mute testimony to the truth or 
falsity of the nebular hypothesis. 

Scattered over the sky we find vast inchoate masses The raw 
of faintly gleaming matter, some of the most stupendous 
of which are revealed by photography alone, being too 
faint for the most powerful visual apparatus. Surely 
here is the raw material which the theory demands. 



material. 



33° 



A Study of the Sky. 



The next step. 



The nebula 
in Orion. 



Planetary 
nebulae. 



The next step in the process is illustrated by the great 
nebula in Andromeda, in the center of which is a bright 
globe. The surrounding matter is arranged in rings or 
whorls, as if there were a motion of rotation, disengag- 
ing rings of tenuous matter. Has any of the disengaged 
material assumed a spherical form ? Look again at this 
wonderful nebula and see the two outlying globes. 

Study the latest photograph of the nebula in Orion, 
and let the gigantic spiral tell its own story. See the 
stars in the Trapezium, and the dark space in which they 
lie, as if some of the nebulous matter had been used up 
in forming them. Examine their spectra and behold 
the bright lines, which tally with lines in the spectrum 
of the nebula. Does not a heated gas produce a spec- 
trum of bright lines ? 

Pass in review hundreds of planetary nebulae. Are 
they not circular ? Have not some of them faint con- 
densations in their centers ? Have not some brighter 
condensations ? Do not a considerable number exhibit 
a spiral structure ? Can we not arrange known nebulae 
in orderly sequence from those composed of the dim- 
mest world-stuff up to those which have justly received 
the appellation of nebulous stars ? Is the testimony of 
the nebulae inconclusive ? We turn to the stars. 

Let us study various photographs of the Pleiades. 
Why does a nebulous bridge run from this faint star to 
its neighbor if there be no relation between nebulae and 
stars? Why does this other nebulous ray connect a row 
of small stars ? Why are so many of the brighter stars 
apparently involved in nebulosity ? Why do rays run 
out from this large nebula to these faint stars ? 
other associ- Why are there so many stars all over the heavens 

and n s S tars nebulae wmcn appear to be enveloped with nebulous matter? 
How are certain very complicated stellar spectra to be ex- 



The Pleiades. 



The NebulcB. 331 



plained ? Are not the stars giving them surrounded by 
enormous gaseous envelopes ? 

Has not our attention been already called to the fact Is there a 
that almost all stars can be arranged in a sequence from sequence? 
planetary nebulae onward to the most highly finished 
orbs n according to the characteristics of their spectra? 
While this is true, let us be candid and admit that such 
a sequence must be considered only as a possible hint of 
progressive development. 

Is the testimony of the nebulae and stars insufficient ? 
We turn to the earth. 

Is the earth a cold, dark, solid body, far removed in 

' J ' . The earth. 

nature from the heated objects which we have consid- 
ered thus far ? Take a thermometer down deep holes in 
the earth's crust, and see the column of mercury slowly 
rise. Listen to the rumbling of yonder volcano; see the 
steamy cloud rising from it, and the scorching outpour- 
ings which have rolled down its sides ; ask the geologist 
whether the granite of our mountains has ever passed 
through primeval fires. Give heed to his statement that 
statuary marble is limestone transformed by heat. Is 
there not a preponderance of evidence in favor of the 
view that mountain chains are wrinkles of the earth's 
crust formed while it was contracting ? Is there no hint 
in the fact that if the earth were heated to incandescence 
its spectrum would resemble the sun's ? 

Is the testimony of the nebulae, the stars, and the 
earth inconclusive ? We turn to the moon. 

He who examines the moon with a telescope and The moon, 
studies its formations will hardly deny that indications 
of an igneous origin are written in large characters over 
its scarred visage. On this point let us listen to Nasmyth 
and Carpenter, two English students of the moon : 

We trust then that we, on our part, have shown that the 



332 A Study of the Sky. 

study of the moon may be a benefit not merely to the astrono- 
mer, but to the geologist, for we behold in it a mighty medal 
A medal of of creation, doubtless formed of the same material and struck 

with the same die that molded our earth, but while the dust of 
countless ages and the action of powerful disintegrating and 
denuding elements have eroded and obliterated the earthly 
impressions, the superscriptions on the lunar surface have re- 
mained with their pristine clearness unsullied, every vestige 
sharp and bright as when it left the Almighty Maker's hand. 

Is the testimony of the nebulae, the stars, the earth, 
and the moon insufficient ? We turn to the planetary 
system, and group some observed harmonies under four 
heads. 

I. Jupiter, Saturn, Uranus, and Neptune are large 
bodies of small density. According to the nebular 
theory were they not formed from large rings of small 
density? Mars, the earth, Venus, and Mercury, on the 
other hand, are small bodies of great density. 

II. All the planets revolve eastward about the sun, 
their orbits being nearly circular, and lying nearly in the 
same plane. 

III. All the known rotations of the planets are east- 
ward, the planes of their equators being nearly coinci- 
dent with those of their orbits. 

IV. The satellites of the planets revolve in planes 
which do not deviate much from the equators of their 
primaries ; they also revolve in the direction in which 
their primaries rotate. The positions of the planes of 
the equators of Uranus and Neptune are, however, un- 
known. 

Is the testimony of the nebulae, the stars, the earth, 

the moon, and the planetary systems insufficient ? We 

turn to the sun. 

The sun It has been stated that the sun's outpour of radiant 

energy is accounted for by the supposition that it is 



The Nebula. 333 



slowly contracting in bulk. If it is contracting, was it 
not larger one thousand years ago than to-day ? Was it 
not still larger one hundred thousand years ago ? Can 
we not go back in thought through the long ages of 
which geologists tell us, and see the sun larger yet and 
more diffuse ? If we may be bold to peer into appalling 
abysses of past time, do we not at last see in dim out- 
line the mists of a gigantic nebula, from which the solar 
system has been formed by such a process as we have 
sketched ? 

Is not the chain of evidence so complete as to compel 
our assent ? If this were a matter of ordinary business, we say ? 
if shares of stock in the nebular hypothesis were for sale, 
would you not consider them a good investment ? 

If you were to consult an astronomer, before making 
this intellectual investment, what would he say ? He mer's opinion, 
would reply that if you wished to invest in an hypothe- 
sis, he could heartily recommend the nebular hypothesis; 
he himself had taken stock in it. But he would beg 
you to remember that there is a vast difference between 
an hypothesis and an ascertained fact, and that this 
particular hypothesis could never attain the certainty of 
a demonstration. He would remind you that a man 
who has a limitless duration of time to draw upon, and 
an infinite extent of space to put the creations of his 
imagination in, ought to be able to invent a far-reaching 
theory which would seemingly agree with almost any 
orderly series of facts. Though it does not now seem at throw of the 



all probable, yet it is possible that in the centuries to 
come new facts may be discovered and new laws formu- 
lated, to which the nebular hypothesis will be compelled 
to yield, as the Ptolemaic theory yielded after fourteen 
centuries to the Copernican, and as Newton's corpuscu- 
lar theory of light gave way to the wave theory. 



theorv. 



334 



A Study of the Sky. 



The subtlety 
of nature. 



A glance ahead. 



The stars 
die out. 



Some day the wreck of the nebular hypothesis may 
furnish a fresh illustration of the doctrine of Bacon that 
the subtlety of nature transcends in many ways the 
subtlety of the intellect and senses of man, and may call 
men's attention anew to the real depth of their igno- 
rance concerning the fundamental causes of natural 

phenom en a . 
Across the 
chasm of centu- 
ries still rings 
the old poetic 
outburst, ' ' Lo, 
these are parts 
of His ways ; 
but how little a 
portion is heard 
of him ? but the 
thunder of his 
power who can 
understand ? ' ' 

We have been 
threading the 
mazes of the 
past : what shall 
we say of the 
future ? In the 
chapter on the sun we have already considered the 
future of the solar system, and we now turn to the 
sidereal universe. 

The stars seem to be radiating away their stores of 
energy, just as the sun is. The best light that we have 
reveals Arcturus the magnificent or Sirius the glowing 
as a dull cold corse, when ages have rolled away. If 
these stellar princes are at last to sink into eternal night, 




Fig. 144. — The Ring Nebula in Lyra. 



The Nebula. 335 



New ones ap- 



Why repine r 



shall we not prophesy the same fate for the lesser orbs ? 
To be sure, their places may be filled by new stars 
condensed from nebulae now seen and from others which P ear and die 

in turn. 

are not yet bright enough to show themselves. But 
the death knell of these new worlds must be sounded at 
last, unless there be some intervention of which we have 
no hint. 

If such be the fate of the sidereal universe, why 
should we repine ? If our reasoning be correct the 
human race will perish long before the sidereal universe 
loses the splendid energies whose manifestations bring 
us so much delight. We have no evidence that there 
are inhabitants of other worlds, who would be over- 
whelmed in the universal rout. The peopling of planets 
surrounding other suns with intelligences is but a vagary 
of the fancy. 

If the Creator spoke the universe into existence, may 
he not speak it out of existence, when once it has ful- is supreme- 
filled his purposes ? But let us call a halt, ere we wander 
further in paths of groundless and fruitless speculation. 
We may rest in the assurance that He who has con- 
trolled the worlds for ages past still holds them in the 
hollow of His hand, and orders their destinies aright. 
Radiant suns are not needed to shed light and heat 
upon the City Beautiful, whose walls are jasper and 
whose gates are pearl. " For the glory of God doth 
lighten it and the Lamb is the light thereof." 



The Creator 



INDEX. 



Achromatic telescope, 131. 

Adam, 17, 20. 

Adams, J. C, 269. 

^Esculapius, 107. 

Age of the sun, 204. 

Albireo, 98. 

Alcor, 45, 60. 

Alcyone, 73. 

Aldebaran, 53, 72. 

Algol, 81, 305, 313. 

"Almagest," 24, 26. 

Alpha Centauri, 305. 

Alphabet, Greek, 55. 

Alphonso, 26. 

Altair, 53, 105. 

Andromeda, 37, 39, 48, 69, 324, 330. 

Andromedes, 290, 292. 

Angular measurement, 41. 

Antares, 53, 101, 102. 

Apennines, 214, 216. 

Aphelion, 237. 

Aquarius, 66. 

Aquila, 53, 105. 

Arabian astronomy, 25. 

Arcturus, 36, 53, 87. 

Aries, 70. 

Arion, 104. 

Aristotle, 23. 

Aryans, 20. 

Asteroids, 39, 246. 

Astronomers, in. 

Auriga, 76. 

Australian savages, 52. 

Babylonian astronomy, 22. 

Bacon, 128. 

Barnard, E. E., 120, 250, 259, 264. 

Bayer, 53. 

Bede, 50. 

Betelgeuse, 53, 74, 75. 

Biela's comet, 281, 284, 293. 

Binary stars, 306. 

Bloomington, 299. 



Bode's law, 247. 

Bootes, 53, 87. 

Brashear, J. A., 137. 

Bread, 180. 

Brenham township, 299. 

Brightness of stars, 57. 

Brooks, W. R., 286, 287. 

Burnham, S. W., 126. 

Campbell, W. W., 245. 

Canals of Mars, 240. 

Cancer, 83, 94. 

Canis Major, 83. 

Canis Minor, 85. 

Capella, 36, 37, 76, 77, 84, 305. 

Capricornus, 109. 

Capture of comets, 273. 

Cassiopeia, 48, 62. 

Castor, 79. 

Catalogue of stars, 54, 55. 

Celestial meridian, 152. 

Celestial sphere, 41, 42, 47. 

Cepheus, 48, 49, 108, 109. 

Ceres, 248, 250. 

Cetus, 49, 69, 71. 

Challis, Professor, 270. 

Chamberlin Observatory, 145. 

Chamberlin telescope, 141. 

Chandler, S. C, 125. 

Chinese astronomy, 21, 93. 

Chromosphere, 189. 

Chronograph, 157, 171. 

Chronometer, 169. 

Clark, A. G., 84, 307. 

Clocks, 146, 172. 

Clusters, 314. 

Coal, 179. 

Coma Berenices, 89. 

Comet-groups, 274. 

Comet hunters, 114, 271. 

Comets, 39, 271. 

Conjunction, 231, 23-. 

Constellations, 48. 



337 



338 



hidex. 



Copernicus, 26, 32, 212. 

Corona, 193, 230. 

Corona Borealis, 92. 

Coronium, 195. 

Corvus, 91. 

Craters, 212. 

Cygnus, 98. 

Declination, 55. 

Declination axis, 139. 

Deimos, 238. 

Delphinus, 104. 

Deneb, 98. 

Diameter of a planet, 160. 

Diffraction grating, 165. 

Dipper, the Great, 36, 60, 61. 

Dipper, the Little, 44, 61. 

Distance of the sun, 181. 

Dollond, John, 131. 

Dome, 148. 

Double stars, 123, 160, 306. 

Draco, 99. 

Druids, 52. 

Duration of life on the earth, 204. 

Earth shine, 209. 

Eclipses, 224. 

Ecliptic, 51. 

Egyptians, 21. 

Ellipse, 273. 

Elongation, 232. 

Encke's comet, 283. 

Envelopes, 276. 

Epicycles, 25. 

Equator, celestial, 55. 

Equinox, 55, 69. 

Faculcz, 189. 

Flamsteed, 54. 

Fomalhaut, 67. 

Galaxy, see Milky Way. 

Galileo, 30, 128, 259. 

Galle, 270. 

Gauss, 248. 

Gemini, 79. 

Gould, B. A., 116. 

Graduations, 150, 156. 

Gravitation, 33, 306. 

Great Plague, 29. 

Grecian philosophers, 22. 

Greek alphabet, 55. 

Guinand, 131. 

Habitability of Mars, 245. 

Hall, Asaph, 238. 



Hall, Chester Moor, 131. 

Heat of the sun, 198, 201. 

Helium, 192, 323. 

Hercules, 53, 96, 315, 319. 

Herodotus, 21. 

Herschel, Caroline, 64, 266. 

Herschel, William, 35, 64, 265. 

Hesiod, 51. 

Hindus, 52, 229. 

Hipparchus, 23, 25, 86. 

Holden, E. S., 114. 

Holmes's comet, 282. 

Huyghens. 260. 

Hyades, 51, 72, 74. 

Hydra, 92. 

Hyperbola, 273. 

Inferior planets, 231. 

Inquisition, 31. 

Iroquois Indians, 49. 

Josephus, 20. 

Judas Iscariot, 210. 

Juno, 248, 250. 

Jupiter, 31, 39, 128, 202, 237, 250, 253, 

273, 328, 332. 
Kant, 327. 

Keeler, James E., 121, 255, 263. 
Kepler, 29. 
Krakatoa, 217. 
Lacus Solis, 243. 
Lagrange, 35. 
Lalande, 54. 
Laplace, 34, 286, 327. 
Laws, Kepler's, 30, 33. 
Laws, Newton's, 33, 34, 273. 
Leo, 86, 291. 
Leonids, 291, 294. 
Lepus, 85. 
Level, 151. 
Leverrier, 269. 
Lexell's comet, 286. 
Libra, 103. 

Lick Observatory, 155. 
Lick telescope, 16, 259. 
Lippershey, 128. 
Lyra, 54, 95, 319. 
Madrid, 300. 
Magellanic clouds, 326. 
Magnetic storms, 199. 
Magnitudes of stars, 57. 
Mark Twain, 204. 
Mars, 27, 29, 39, 236, 250, 329. 



Index. 



339 



Maxwell, Clerk, 263. 

Mercury, 39, 231. 

Meridian circle, 145, 149, 150, 152, 154. 

Meteoric showers, 284, 290, 294. 

Meteorites, 293, 294. 

Meteors, 39, 288. 

Mexicans, 52. 

Micrometer, 124, 158, 272. 

Milk-dipper, 108. 

Milky Way, 17, 18, 31, 38, 99, 301, 316, 

321. 
Mira, 72, 314. 

Mizar, 44, 45, 46, 60, 61, 62, 305. 
Moon, 36, 205. 
Motion of the heavens, 36. 
Mountains of the moon, 214. 
Mounting of a telescope, 138, 139. 
Multiple stars, 309. 
Nebulae, 39, 271, 321. 
Nebular theory, 327. 
Neptune, 39, 268, 329, 332. 
Newcomb, S., 115. 
Newton, Isaac, 32, 119, 125, 129, 130. 
Nova Aurigae, 78, 312. 
Object-glass, 138, 153. 
Observatories, 143. 
Okouari, 49. 
Olbers, 248. 
Ophiuchus, 106. 
Opposition, 237. 

Orion, 39, 53, 74, 102, 321, 323, 325. 
Pallas, 248, 250. 
Parabola, 273. 
Pare, 280. 
Pegasus, 49, 64. 
Perihelion, 237. 
Periodicity of sun-spots, 186. 
Perseids, 290, 291. 
Perseus, 49, 81. 
Persians, 52. 
Personal equation, 170. 
Peruvians, 52. 

Phases of inferior planets, 232. 
Phobos, 238. 
Photography, 165, 329. 
Photosphere, 187. 
Piazzi, 247, 248. 
Pickering, E. C, 60, 117. 
Pickering, YV. H., 119. 
Pisces, 68. 
Planetary system, 39, 332. 



Pleiades, 37, 51, 72, 319, 323, 330. 

Pointers, 41. 

Polar axis, 139. 

Pole, celestial, 43, 62. 

Pole-star, 41, 61, 62. 

Pollux, 79. 

Procyon, 85. 

Prominences, 190, 230. 

Proper motion, 319. 

Ptolemaic system, 24. 

Ptolemy, 24, 59. 

Pythagoras, 22, 23. 

Radiant, 289. 

Red spot on Jupiter, 255. 

Reflector, 130. 

Refraction, 218. 

Refractor, 131. 

Regulus, 86. 

Reticle, 151. 

Rigel, 75- 

Right ascension, 55. 

" Rigveda," 20. 

Rosse, 130. 

Sagitta, 100. 

Sagittarius, 109, 323. 

Satellites, 40. 

Saturn, 39, 259, 328, 332. 

Schaeberle, J. M., 197. 

Schiaparelli, 233, 240, 241. 

Schwabe, 186. 

Scientific method, 20. 

Scorpio, 101. 

Serpens, 106. 

Serpentarius, see Ophiuchus. 

Sextant, 223. 

Shadow of the earth, 15. 

Shooting stars, 288. 

Showers, meteoric, 284, 290, 294. 

Sirius, 36, 37, 53, 74, 84, 304, 307. 

Site of an observatory-, 143. 

Society Islanders, 51. 

Solstice, 79. 

Spectroscope, 162. 

Spectrum analysis, 163. 

Sphere, celestial, 41, 42, 47. 

Spica, 90, 91, 309. 

Spider-webs, 161. 

Standard time, 16S, 174. 

Star-light, 305. 

Starry skies, 15. 

Stars, 3S, 301. 



340 



Index. 



Structure of the universe, 318. 

Sun, 179. 

Sun-spots, 182. 

Superior planets, 237. 

Swift, Lewis, 230, 287. 

Swift's comet, 278. 

Taurus, 54, 72. 

Telescope, 128, 141. 

Temporary stars, 311. 

Tides, 205, 223. 

Time, 117, 167, 223. 

Transit, 231. 

Trapezium, 76, 325, 330. 

Tycho, 28, 29, 32, 63, 311. 

Types of stellar spectra, 309. 

Uranienburg, 29. 

Uranus, 39, 247, 265, 268, 329, 332. 

Ursa Major, 59. 



Ursa Minor, 61. 

Variable stars, 310, 311. 

Vega, 36, 37, 62, 95, 305. 

Venus, 31, 37, 38, 39, 128, 231, 234; 253. 

Vernal equinox, 55, 69. 

Vesta, 248, 250. 

Vesuvius, 215. 

Virgo, 90, 104. 

Volcanoes, 215. 

Watches, 176. 

Watson, J. C, 230. 

Weather, 201, 225. 

Weigel, Professor, 50. 

World's Fair, 211, 296. 

Yerkes Observatory, 144. 

Young, Charles A., 112, 191, 200. 

Zodiac, 50, 51. 

Zodiacal light, 294. 



